Fix memory leak in connection string validation.

Introduced in commit c3afe8cf5a.

Discussion: https://postgr.es/m/066a65233d3cb4ea27a9e0778d2f1d0dc764b222.camel@j-davis.com
Reviewed-by: Nathan Bossart, Tom Lane
Backpatch-through: 16

src/backend/replication/libpqwalreceiver/libpqwalreceiver.c

@@ -284,11 +284,16 @@ libpqrcv_check_conninfo(const char *conninfo, bool must_use_password)
 		}
 
 		if (!uses_password)
+		{
+			/* malloc'd, so we must free it explicitly */
+			PQconninfoFree(opts);
+
 			ereport(ERROR,
 					(errcode(ERRCODE_S_R_E_PROHIBITED_SQL_STATEMENT_ATTEMPTED),
 					 errmsg("password is required"),
 					 errdetail("Non-superusers must provide a password in the connection string.")));
 		}
+	}
 
 	PQconninfoFree(opts);
 }