fix issue #1469 - glitches with type-naming

Issue reported by ars3niy:  assigning names to types of objects,
or clearing such, did not update persistent inventory window.  Also,
the sequence
  assign-a-name,
  name-as-' '-to-unname,
  assign-a-name again,
  unname again
would result in impossible: "named object not in disco".

This fixes the impossibility.  The fix for #1470 has already taken
care of the presistent inventory issue.

Fixes #1469

doc/fixes3-7-0.txt

@@ -2168,6 +2168,9 @@ livelog/#chronicle for bribing a demon lord reported random monster and
 livelog/#chronicle for saving-grace: if saving-grace prevents hero's death,
 	report it [at present, it uses the livelog classification for breaking
 	a conduct]
+naming a type of item, unnaming it (with name of <space>), naming it again
+	(new name or re-use of old one), then unnaming it again would issue
+	impossible: "named object not in disco"
 
 
 Fixes to 3.7.0-x Platform and/or Interface Problems Exposed Via git Repository

src/o_init.c

@@ -488,7 +488,7 @@ discover_object(
 void
 undiscover_object(int oindx)
 {
-    if (!objects[oindx].oc_name_known) {
+    if (!objects[oindx].oc_name_known && !objects[oindx].oc_encountered) {
         int dindx, acls = objects[oindx].oc_class;
         boolean found = FALSE;
 
@@ -510,7 +510,6 @@ undiscover_object(int oindx)
 
         if (objects[oindx].oc_class == GEM_CLASS)
             gem_learned(oindx); /* ok, it's actually been unlearned */
-        update_inventory();
     }
 }