read-cache: mark new entries for split index

Make sure entry addition does not lead to unifying the index. We don't
need to explicitly keep track of new entries. If ce->index is zero,
they're new. Otherwise it's unlikely that they are new, but we'll do a
thorough check later at writing time.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

read-cache.c

@@ -38,7 +38,8 @@ static struct cache_entry *refresh_cache_entry(struct cache_entry *ce,
 #define CACHE_EXT_LINK 0x6c696e6b	  /* "link" */
 
 /* changes that can be kept in $GIT_DIR/index (basically all extensions) */
-#define EXTMASK (RESOLVE_UNDO_CHANGED | CACHE_TREE_CHANGED)
+#define EXTMASK (RESOLVE_UNDO_CHANGED | CACHE_TREE_CHANGED | \
+		 CE_ENTRY_ADDED)
 
 struct index_state the_index;
 static const char *alternate_index_output;