Blessed potion of polymorph asks user for monster to poly into

... unless there's some other form that would override the choice,
such as a worn dragon armor, lycanthropy, or vampirism.

The polymorph will be in effect for 10-24 turns.

src/fountain.c

@@ -632,7 +632,7 @@ drinksink(void)
         pline("This %s contains toxic wastes!", hliquid("water"));
         if (!Unchanging) {
             You("undergo a freakish metamorphosis!");
-            polyself(0);
+            polyself(POLY_NOFLAGS);
         }
         break;
     /* more odd messages --JJB */