When perspective control line editing is active and the history entry is
changed such that edit mode is automatically disabled, there is a crash.
The history change triggers a processing parameters update and disables
editing. When editing is disabled, the perspective tool also tries to
update the processing parameters, causing a double mutex lock attempt.
This commit avoids updating parameters from the perspective tool and
uses the tweak operator (introduced with the spot removal tool) to achieve
the same effect.
Closes#6251.
