revision: fix memory leak in prepare_show_merge()

In revision.c:prepare_show_merge(), we allocated an array in prune
but forget to free it. Since parse_pathspec is not responsible to
free prune, we should add `free(prune)` in the end of prepare_show_merge().

Signed-off-by: Lidong Yan <502024330056@smail.nju.edu.cn>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

revision.c

@@ -2068,6 +2068,7 @@ static void prepare_show_merge(struct rev_info *revs)
 	parse_pathspec(&revs->prune_data, PATHSPEC_ALL_MAGIC & ~PATHSPEC_LITERAL,
 		       PATHSPEC_PREFER_FULL | PATHSPEC_LITERAL_PATH, "", prune);
 	revs->limited = 1;
+	free(prune);
 }
 
 static int dotdot_missing(const char *arg, char *dotdot,

t/t7007-show.sh

@@ -167,4 +167,28 @@ test_expect_success 'show --graph is forbidden' '
   test_must_fail git show --graph HEAD
 '
 
+test_expect_success 'show unmerged index' '
+	git reset --hard &&
+
+	git switch -C base &&
+	echo "base" >conflicting &&
+	git add conflicting &&
+	git commit -m "base" &&
+
+	git branch hello &&
+	git branch goodbye &&
+
+	git switch hello &&
+	echo "hello" >conflicting &&
+	git commit -am "hello" &&
+
+	git switch goodbye &&
+	echo "goodbye" >conflicting &&
+	git commit -am "goodbye" &&
+
+	git switch hello &&
+	test_must_fail git merge goodbye &&
+	git show --merge HEAD
+'
+
 test_done