Add unreachable "break" to satisfy -Wimplicit-fallthrough.

gcc is a bit pickier about this than perhaps it should be.

Discussion: https://postgr.es/m/E1h6zzT-0003ft-DD@gemulon.postgresql.org

src/backend/parser/parse_func.c

@@ -2332,6 +2332,7 @@ LookupFuncWithArgs(ObjectType objtype, ObjectWithArgs *func, bool missing_ok)
 																  NIL, argoids))));
 						break;
 				}
+				break;
 
 			case FUNCLOOKUP_AMBIGUOUS:
 				switch (objtype)