Don't check ferror(NULL) when the new file has been

succesfully saved and closed.

src/server/simple-cache.c

@@ -1546,7 +1546,7 @@ sync_part(void)
 	restart_kom("sync(): sync_state==%d", sync_state);
     }
 
-    if ( ferror(file_b) != 0)
+    if ( file_b != NULL && ferror(file_b) != 0)
 	sync_state = sync_error;
 
     return FALSE;