pack-bitmap.c: do not ignore error when opening a bitmap file

Calls to git_open() to open the pack bitmap file and
multi-pack bitmap file do not report any error when they
fail.  These files are optional and it is not an error if
open failed due to ENOENT, but we shouldn't be ignoring
other kinds of errors.

Signed-off-by: Teng Long <dyroneteng@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

pack-bitmap.c

@@ -317,10 +317,13 @@ static int open_midx_bitmap_1(struct bitmap_index *bitmap_git,
 	char *bitmap_name = midx_bitmap_filename(midx);
 	int fd = git_open(bitmap_name);
 
-	free(bitmap_name);
-
-	if (fd < 0)
+	if (fd < 0) {
+		if (errno != ENOENT)
+			warning_errno("cannot open '%s'", bitmap_name);
+		free(bitmap_name);
 		return -1;
+	}
+	free(bitmap_name);
 
 	if (fstat(fd, &st)) {
 		close(fd);
@@ -376,10 +379,14 @@ static int open_pack_bitmap_1(struct bitmap_index *bitmap_git, struct packed_git
 
 	bitmap_name = pack_bitmap_filename(packfile);
 	fd = git_open(bitmap_name);
-	free(bitmap_name);
 
-	if (fd < 0)
+	if (fd < 0) {
+		if (errno != ENOENT)
+			warning_errno("cannot open '%s'", bitmap_name);
+		free(bitmap_name);
 		return -1;
+	}
+	free(bitmap_name);
 
 	if (fstat(fd, &st)) {
 		close(fd);