Suppress MSVC warning in typeStringToTypeName function.

MSVC doesn't realize ereport(ERROR) doesn't return.

David Rowley

src/backend/parser/parse_type.c

@@ -792,6 +792,7 @@ fail:
 	ereport(ERROR,
 			(errcode(ERRCODE_SYNTAX_ERROR),
 			 errmsg("invalid type name \"%s\"", str)));
+	return NULL; /* keep compiler quiet */
 }
 
 /*