Revert "Flip IOP: modify_roi_in(): drop sanity check"

This reverts commit 3484731e3295f619bb99d41b3a12ba39e5c78919.
Flip IOP: modify_roi_in(): sanity check: do not use iwidth/iheight but buf_in.width/buf_in.height

iwidth/iheight is the size of original input buffer, which is correct
only if there is nothing in between changing the roi (like scalepixels, flip)
Clipping IOP: modify_roi_in(): redo sanity check
This fixes following issue: when scalepixels iop is active, after activating c&r image is "cut in half" with the bottom half black.

NOTE: if there is no "sanity check.", there is a crash in dt_interpolation_resample
Lens IOP: do not use iwidth/iheight but buf_in.width/buf_in.height

iwidth/iheight is the size of original input buffer, which is correct
only if there is nothing in between changing the roi (like scalepixels)