Check for infinite recursion

I spent about 4 hours trying to track down why a sub target had a target of a super target and could not figure it out. In the mean time, this check will exit out of endProcessing if this case happens, avoiding a stackoverflow crash.

I've also noticed that calling removeAllTargets and adding new targets can affect the frame buffer size and appearance of other unrelated filters, but after several hours have had no luck tracking down the cause of that either. I noticed this particularly with the toon and emboss filters.

I suggest diffing this with ?w=1