[PATCH 3/3] diff: turn off skip_stat_unmatch on "diff --cached"

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

skip_stat_unmatch flag is added in fb13227 (git-diff: squelch "empty"
diffs - 2007-08-03) to ignore empty diffs caused by stat-only
dirtiness. In "diff --cached" case, stat is not invovled at all. While
the code is written in a way that no expensive I/O is done, we still
need to move all file pairs from the old queue to the new queue in
diffcore_skip_stat_unmatch(). Avoid it.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 builtin/diff.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/builtin/diff.c b/builtin/diff.c
index 0f247d2..85f97d7 100644
--- a/builtin/diff.c
+++ b/builtin/diff.c
@@ -150,9 +150,10 @@ static int builtin_diff_index(struct rev_info *revs,
 			perror("read_cache_preload");
 			return -1;
 		}
-	} else if (read_cache() < 0) {
-		perror("read_cache");
-		return -1;
+	} else {
+		if (read_cache() < 0)
+			return error("read_cache: %s", strerror(errno));
+		revs->diffopt.skip_stat_unmatch = 0;
 	}
 	return run_diff_index(revs, cached);
 }
-- 
1.8.5.2.240.g8478abd