filter out nulls for array_flip

Array flip throws a warning if a value is not a string or an integer. I was uploading a pdf where the height and width values were null causing this warning.
Merge pull request #164 from styks1987/master

filter out nulls for array_flip
Clean up meta data loop
Fix operand error [#162]
Fix associated transform images not being deleted [#163]
4.5.1
Update AttachmentBehavior.php
Update AttachmentBehavior.php

Delete all Attachment fields when doing update.
Merge pull request #166 from dilab/master

Update/Delete all fields' files
4.5.2
Merge branch 'master' of github.com:milesj/uploader
Merge branch 'master' of github.com:nielin/Uploader

Signed-off-by: Niel Vanterpool <nielingroup@gmail.com>

Conflicts:
	Model/Behavior/AttachmentBehavior.php