stash: fix segmentation fault when files were added with intent

After `git add -N <file>`, the index is in a special state. A state for
which the built-in stash was not prepared, as it failed to initialize
the `rev` structure in that case before using `&rev.pending`.  If
`reset_tree()` returns a non-zero value, `stash_working_tree()`
calls `object_array_clear()` with `&rev.pending`.  If `rev` is not
initialized, this causes a segmentation fault.

Prevent this by initializing `rev` before calling `reset_tree()`.

This fixes #2006.

[jes: modified the commit message in preparation for sending this patch
to the Git mailing list.]

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

builtin/stash.c

@@ -1050,14 +1050,15 @@ static int stash_working_tree(struct stash_info *info, struct pathspec ps)
 	struct strbuf diff_output = STRBUF_INIT;
 	struct index_state istate = { NULL };
 
+	init_revisions(&rev, NULL);
+
 	set_alternate_index_output(stash_index_path.buf);
 	if (reset_tree(&info->i_tree, 0, 0)) {
 		ret = -1;
 		goto done;
 	}
 	set_alternate_index_output(NULL);
 
-	init_revisions(&rev, NULL);
 	rev.prune_data = ps;
 	rev.diffopt.output_format = DIFF_FORMAT_CALLBACK;
 	rev.diffopt.format_callback = add_diff_to_buf;

t/t3903-stash.sh

@@ -287,6 +287,14 @@ test_expect_success 'stash an added file' '
 	test new = "$(cat file3)"
 '
 
+test_expect_success 'stash --intent-to-add file' '
+	git reset --hard &&
+	echo new >file4 &&
+	git add --intent-to-add file4 &&
+	test_when_finished "git rm -f file4" &&
+	test_must_fail git stash
+'
+
 test_expect_success 'stash rm then recreate' '
 	git reset --hard &&
 	git rm file &&