A proper fix for the not-saved Move Tool action when it is saved while the stroke is active

This patch uses more accurate way of locking the image:

o When the autosave is happening and the document cannot lock the image,
the document sets the autosave interval to 10s to catch the nearest
moment when there is no stroke active

o When the usual saving is happening, the document first requests the end
of the current stroke, then tries to lock the image again