Fix PQExpBuffer leak in oid dumping

Commit f51f2f57 backported upstream commit caddcb8f
but missed one destroyPQExpBuffer() call in the merge. Add to avoid
a tiny leak in the early exit path and to align us with upstream.

src/bin/pg_dump/pg_dump.c

@@ -8344,6 +8344,7 @@ dumpOpfamily(Archive *fout, OpfamilyInfo *opfinfo)
 			destroyPQExpBuffer(query);
 			destroyPQExpBuffer(q);
 			destroyPQExpBuffer(delq);
+			destroyPQExpBuffer(labelq);
 			return;
 		}