Some fixes for the PHP backend

The PHP backend  never create the final file. 

Example  with a file of 7837873 bytes : 
 * chunk 1
     * chunk size : 1048576 (from `$_POST['resumableChunkSize']`)
     * HTTP  Content-Length : 1049640 
 * chunk 2-6.. The same
 * chunk 7
     * Last chunk !
     * chunk size : 1048576 (from `$_POST['resumableChunkSize']`) < Wrong !
     * HTTP Content-Length : 1547481 
     *  `if ($total_files * $chunkSize >=  $totalSize)`
         * `$total_files * $chunkSize` : 7340032 
         * `$totalSize` :7837873

We have : `chunkSize < lastChunkSize < 2*chunkSize`
So the fix is just : ` $total_files * $chunkSize >=  $totalSize - $chunkSize + 1.`

I have also deleted all `@` because it's the evil.

My 2 cents