BulkStatus should correctly report the error count

When a bulk status delta reports an error count, its merged with the overall bulk status.

Currently a counter is incremented instead of adding the error to the count.

ie. BulkStatus Line 205

if (update.errorCount > 0) {
    errorCount++;
}

should be:

if (update.errorCount > 0) {
    errorCount += update.errorCount;
}

In my test I had 50 errors but only 4 were being reported.