objc version generates wrong diffs

```
What steps will reproduce the problem?
* compile and run:
int main(int argc, const char * argv[]) {
@autoreleasepool {
NSString *oldstr = @"MLNQRSTUVWX";
NSString *newstr = @"ABCDEFBGHIJKLMLNOPRQGYZ!";
DiffMatchPatch *dmp = [[DiffMatchPatch alloc] init];
NSMutableArray *diffs = [dmp diff_mainOfOldString:oldstr andNewString:newstr checkLines:NO];
NSString *text2 = [dmp diff_text2:diffs];
NSLog(@"%@", [oldstr isEqualToString:text2] ? @"OK" : @"ERR");
}
}

What is the expected output? What do you see instead?
* expected: OK
* see: ERR

What version of the product are you using? On what operating system?
* diff_match_patch_20121119.zip, OS X Yosemite

Please provide any additional information below.

```

Original issue reported on code.google.com by `hbhf...@gmail.com` on 27 Feb 2015 at 10:23