Merge pull request #202 from infinitespace-studios/fixnullbug

Add missing NULL check in zip_stat_index.
diff --git a/lib/zip_stat_index.c b/lib/zip_stat_index.c
index 0f8bead..62dc045 100644
--- a/lib/zip_stat_index.c
+++ b/lib/zip_stat_index.c
@@ -55,7 +55,7 @@
             return -1;
         }
 
-        if (entry->changes->changed & ZIP_DIRENT_LAST_MOD) {
+        if (entry->changes != NULL && entry->changes->changed & ZIP_DIRENT_LAST_MOD) {
             st->mtime = de->last_mod;
             st->valid |= ZIP_STAT_MTIME;
         }