[PATCH (resend)] ls-files: don't try to prune an empty index

["René Scharfe" <l.s.r@web.de>]

Exit early when asked to prune an index that contains no entries to
begin with.  This avoids pointer arithmetic on istate->cache, which is
possibly NULL in that case.

Found with Clang's UBSan.

Signed-off-by: Rene Scharfe <l.s.r@web.de>
---
Messed up whitespace when sending this the first time.

 builtin/ls-files.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/builtin/ls-files.c b/builtin/ls-files.c
index b8514a0029..adf572da68 100644
--- a/builtin/ls-files.c
+++ b/builtin/ls-files.c
@@ -362,7 +362,7 @@ static void prune_index(struct index_state *istate,
 	int pos;
 	unsigned int first, last;
 
-	if (!prefix)
+	if (!prefix || !istate->cache_nr)
 		return;
 	pos = index_name_pos(istate, prefix, prefixlen);
 	if (pos < 0)
-- 
2.13.3