Temporary directory not cleaned up (regression)

[phloxic]

With recent changes shutil now tries (and fails silently) to remove a tree with path generated here: https://github.com/flavioribeiro/video-thumbnail-generator/blob/master/generator#L195 which is actually the so-called 'prefix' of the temporary png filenames.

shutil instead should try to remove TMP_FRAMES_PATH presumably.

However I am not sure how this fares with the new directory processing feature.
I also don't know in which scenario the TMP_FRAMES_PATH is recreated: https://github.com/flavioribeiro/video-thumbnail-generator/blob/master/generator#L193-L194 (instead of creating a new temporary directory safely).