re PR go/61258 (gccgo: assertion failure go-map-delete.c:37 [GoSmith])

	PR go/61258
runtime: Don't crash when deleting zero-sized key.

From-SVN: r218702

libgo/runtime/go-map-delete.c

@@ -35,7 +35,10 @@ __go_map_delete (struct __go_map *map, const void *key)
   key_descriptor = descriptor->__map_descriptor->__key_type;
   key_offset = descriptor->__key_offset;
   key_size = key_descriptor->__size;
-  __go_assert (key_size != 0 && key_size != -1UL);
+  if (key_size == 0)
+    return;
+
+  __go_assert (key_size != -1UL);
   equalfn = key_descriptor->__equalfn;
 
   key_hash = key_descriptor->__hashfn (key, key_size);