remote: plug memory leak in match_explicit()

The `guess_ref()` returns an allocated buffer of which `make_linked_ref()`
does not take custody (`alloc_ref()` makes a copy), therefore we need to
release the buffer afterwards.

Noticed via Coverity.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

remote.c

@@ -1191,9 +1191,10 @@ static int match_explicit(struct ref *src, struct ref *dst,
 		else if (is_null_oid(&matched_src->new_oid))
 			error("unable to delete '%s': remote ref does not exist",
 			      dst_value);
-		else if ((dst_guess = guess_ref(dst_value, matched_src)))
+		else if ((dst_guess = guess_ref(dst_value, matched_src))) {
 			matched_dst = make_linked_ref(dst_guess, dst_tail);
-		else
+			free(dst_guess);
+		} else
 			error("unable to push to unqualified destination: %s\n"
 			      "The destination refspec neither matches an "
 			      "existing ref on the remote nor\n"