TTY_PERM_INVENT fix header for empty perm_invent

and reimplement 'sparse' mode (TTYINV=2 or TTYINV=3).

When hero had no inventory except for gold and perminv display mode is
ignoring gold, the header said "empty" when "only gold" was intended.

Sparse mode populates perminv with inventory letters in the unused
slots instead of leaving them blank.  (The core doesn't need to be
aware of that since it doesn't affect what display_inventory() sends
to the inventory menu.)

win/tty/wintty.c

@@ -257,7 +257,6 @@ void g_pututf8(uint8 *utf8str);
 #endif
 
 #ifdef TTY_PERM_INVENT
-static char Empty[1] = { '\0' };
 static struct tty_perminvent_cell zerottycell = { 0, 0, 0, { 0 }, 0 };
 static glyph_info zerogi = { 0 };
 static struct to_core zero_tocore = { 0 };
@@ -278,13 +277,14 @@ static int ttyinv_create_window(int, struct WinDesc *);
 static void ttyinv_remove_data(boolean);
 static void ttyinv_add_menu(winid, struct WinDesc *, char ch, int attr,
                             int clr, const char *str);
+static int selector_to_slot(char ch, const int invflags, boolean *ignore);
+static char slot_to_invlet(int, boolean);
 static void ttyinv_render(winid window, struct WinDesc *cw);
 static void tty_invent_box_glyph_init(struct WinDesc *cw);
 static boolean assesstty(enum inv_modes, short *, short *,
                          long *, long *, long *, long *, long *);
 static void ttyinv_populate_slot(struct WinDesc *, int, int,
                                  const char *, int32_t);
-static int selector_to_slot(char ch, const int invflags, boolean *ignore);
 #endif
 
 /*
@@ -3054,8 +3054,14 @@ selector_to_slot(
          * become an in-use item.
          * Inuse_only items might include one (or more than one) with
          * invlet '#' but it isn't special for Inuse_only.
+         * When nothing is in use, the core sends a menu header line to
+         * to indicate such in order to avoid having an empty menu; we
+         * ignore that and reconstruct one in ttyinv_render().
          */
-        slot = inuse_only_start++;
+        if (!ch)
+            *ignore = TRUE;
+        else
+            slot = inuse_only_start++;
     } else {
         /* normal perminv */
         switch (ch) {
@@ -3090,15 +3096,40 @@ selector_to_slot(
     return slot;
 }
 
+static char
+slot_to_invlet(int slot, boolean incl_gold)
+{
+    char res = '\0';
+
+    switch (slot) {
+    case 0:
+        res = incl_gold ? '$' : 'a';
+        break;
+    case 53:
+        /* if (!incl_gold) impossible("ttyinv_render: slot %d?", slot); */
+        res = '#';
+        break;
+    default:
+        if (incl_gold)
+            --slot; /* simplify 1..52 (0 and 53 won't get here) to 0..51 */
+        res = (slot < 26) ? ('a' + slot)
+              : (slot < 52) ? ('A' + slot - 26)
+                : '?'; /* won't happen */
+        break;
+    }
+    return res;
+}
+
 static void
 ttyinv_render(winid window, struct WinDesc *cw)
 {
     int row, col, slot, side, filled_count = 0, slot_limit;
     struct tty_perminvent_cell *cell;
-    char invbuf[BUFSZ], *text;
+    char invbuf[BUFSZ];
     boolean force_redraw = gp.program_state.in_docrt ? TRUE : FALSE,
             show_gold = (ttyinvmode & InvShowGold) != 0,
-            inuse_only = (ttyinvmode & InvInUse) != 0;
+            inuse_only = (ttyinvmode & InvInUse) != 0,
+            sparse = (ttyinvmode & InvSparse) != 0 && !inuse_only;
     int rows_per_side = (!show_gold ? 26 : 27);
 
     slot_limit = SIZE(slot_tracker);
@@ -3118,22 +3149,19 @@ ttyinv_render(winid window, struct WinDesc *cw)
         if (slot_tracker[slot])
            continue;
         if (slot == 0 && !filled_count) {
-            /* FIXME: this isn't correct; it shows "empty" if hero has gold
-               and player hasn't set ttyinvmode to display it; it can also
-               be drawn and briefly seen while other stuff (that player
-               just dropped or used up) hasn't been erased yet */
             Sprintf(invbuf, "%-4s[%s]", "",
-                    !filled_count ? "empty"
-                    : inuse_only  ? "no items are in use"
-                                  : "only gold");
-            text = invbuf;
+                    inuse_only ? "no items are in use"
+                    : (!show_gold && money_cnt(gi.invent)) ? "only gold"
+                      : "empty");
+        } else if (sparse && filled_count) {
+            Sprintf(invbuf, "%c", slot_to_invlet(slot, show_gold));
         } else {
-            text = Empty; /* "" => fill slot with spaces */
+            invbuf[0] = '\0'; /* "" => fill slot with spaces */
         }
         row = (slot % rows_per_side) + 1; /* +1: top border */
         /* side: left side panel or right side panel, not a window column */
         side = slot / rows_per_side;
-        ttyinv_populate_slot(cw, row, side, text, 0);
+        ttyinv_populate_slot(cw, row, side, invbuf, 0);
     }
     /* has there been a glyph reset since we last got here? */
     if (gg.glyph_reset_timestamp > last_glyph_reset_when) {