Fix small memory leaks in GUC checks

Follow-up commit to a9d58bf.  Backpatch down to v16 where
this was added in order to keep the code consistent for future
backpatches.

Author: Tofig Aliev <[email protected]>
Reviewed-by: Daniel Gustafsson <[email protected]>
Reviewed-by: Masahiko Sawada <[email protected]>
Discussion: https://postgr.es/m/[email protected]
Backpatch-through: 16

Author: danielgustafsson

src/backend/commands/variable.c

@@ -1092,6 +1092,8 @@ check_application_name(char **newval, void **extra, GucSource source)
 		return false;
 	}
 
+	guc_free(*newval);
+
 	pfree(clean);
 	*newval = ret;
 	return true;
@@ -1128,6 +1130,8 @@ check_cluster_name(char **newval, void **extra, GucSource source)
 		return false;
 	}
 
+	guc_free(*newval);
+
 	pfree(clean);
 	*newval = ret;
 	return true;