[#29526] YSQL: Don't send custom parse error packet for un-named prep stmt

Summary: This diff avoids sending `YBParsePrepareErrorResponse` packet for un-named prepared statement from backend to connection manager as no entry is made into server hash map for it.

Test Plan:
Jenkins: all tests

**Manually**
Checked connection manager logs for un-named prepared statement on an error no 'YBParsePrepareErrorResponse' packet is received nor 'failed to evict %u hashmap entry from server' message is seen.

Reviewers: skumar, anabaria, vikram.damle, asrinivasan, arpit.saxena

Reviewed By: arpit.saxena

Subscribers: svc_phabricator, arpit.saxena, yql

Differential Revision: https://phorge.dev.yugabyte.com/D48640

Author: Manav Kumar

src/postgres/src/backend/tcop/postgres.c

@@ -6757,7 +6757,13 @@ PostgresMain(const char *dbname, const char *username)
 													  yb_is_dml_command(query_string),
 													  &need_retry);
 						MemoryContextSwitchTo(errorcontext);
-						if (YbIsClientYsqlConnMgr())
+						/*
+						 * YB: Report parse error with the prepared statement name to connection
+						 * manager. This is done so that connection manager can evict the entry
+						 * from the server hashmap as parse has failed. Conn mgr does not record
+						 * any entry for unnamed prepared statement in it's server hashmap.
+						 */
+						if (YbIsClientYsqlConnMgr() && stmt_name[0] != '\0')
 						{
 							pq_puttextmessage('4', stmt_name);
 							pq_flush();