fix missing index update/mocha test

Author: whoozle

core/model.js

@@ -106,7 +106,7 @@ exports.ModelUpdate.prototype.apply = function(view, skipCheck) {
 			apply(ModelUpdateInsert, src, src_n - dst_n)
 			break
 		} else if (dst === src) {
-			apply(row[1]? ModelUpdateUpdate: ModelUpdateNothing, src)
+			apply(row[1] || offset !== 0? ModelUpdateUpdate: ModelUpdateNothing, src)
 			if (offset !== 0)
 				view._updateDelegateIndex(src)
 			++src