Thumbnail generation for JPEG images fail with latest PHP versions (5.4-5.6)

[mmvsk]

After the latest upgrade of PHP (5.6) on one of our client's server, thumbnail generation for JPEG images stopped working.

After some investigation, I found that this bug is caused by an invalid use of the imagejpeg() function in plugins/editor.diaporama/PThumb.lib.php :

According to the PHP documentation of imagejpeg(), the second parameter must be either a valid filename, or null. You use an empty string, but that's invalid (before this argument was silently typecasted).

That breaking change (silent typecast vs. error throwing) was reported here, and was also fixed in another thumbnail generation library.

[mmvsk]

Issue fixed in PR #646