avoid uninit stype (#9832)

Author: uzhastik

ydb/library/yql/sql/pg/pg_sql.cpp

@@ -5852,7 +5852,7 @@ class TExtensionHandler : public IPGParseEvents {
         auto nameNode = ListNodeNth(value->defnames, 0);
         auto name = to_lower(TString(StrVal(nameNode)));
         TString sfunc;
-        ui32 stype;
+        ui32 stype = 0;
         TString combinefunc;
         TString finalfunc;
         TString serialfunc;