init NhRect, before passing to selection_getbounds

selection_getbounds() has a check and early return.
Initialization will ensure a known state if that early return
were ever taken.

This is an alternative approach to pr #1163.

src/sp_lev.c

@@ -4675,7 +4675,7 @@ struct selectionvar *
 selection_not(struct selectionvar *s)
 {
     int x, y;
-    NhRect tmprect;
+    NhRect tmprect = cg.zeroNhRect;
 
     for (x = 0; x < s->wid; x++)
         for (y = 0; y < s->hei; y++)
@@ -4689,7 +4689,7 @@ selection_filter_mapchar(struct selectionvar *ov,  xint16 typ, int lit)
 {
     int x, y;
     struct selectionvar *ret;
-    NhRect rect;
+    NhRect rect = cg.zeroNhRect;
 
     if (!ov)
         return NULL;
@@ -4727,7 +4727,7 @@ selection_filter_percent(
 {
     int x, y;
     struct selectionvar *ret;
-    NhRect rect;
+    NhRect rect = cg.zeroNhRect;
 
     if (!ov)
         return NULL;
@@ -4753,7 +4753,7 @@ selection_rndcoord(
     int idx = 0;
     int c;
     int dx, dy;
-    NhRect rect;
+    NhRect rect = cg.zeroNhRect;
 
     selection_getbounds(ov, &rect);
 
@@ -4794,7 +4794,7 @@ selection_do_grow(struct selectionvar *ov, int dir)
 {
     coordxy x, y;
     struct selectionvar *tmp;
-    NhRect rect;
+    NhRect rect = cg.zeroNhRect;
 
     if (!ov)
         return;
@@ -5222,7 +5222,7 @@ selection_iterate(
     genericptr_t arg)
 {
     coordxy x, y;
-    NhRect rect;
+    NhRect rect = cg.zeroNhRect;
 
     if (!ov)
         return;
@@ -5645,7 +5645,7 @@ lspo_replace_terrain(lua_State *L)
     lua_Integer x1, y1, x2, y2;
     int chance;
     int tolit;
-    NhRect rect;
+    NhRect rect = cg.zeroNhRect;
 
     create_des_coder();