spelling: don't partition the file for replacements in a marked region
Partitioning the file makes the undo system lose track, so that undoing
things has a good chance of losing data. Instead, just make sure that
the region is marked "backwards", with current at the top and the mark
at the bottom, and then let the replace loop take care of not going
outside of the marked region.
This also has the effect that if the marked region fits entirely on the
screen, or all the misspellings are onscreen, then the screen will not
be scrolled at all. Which makes for a smooth experience.
This fixes https://savannah.gnu.org/bugs/?47836,
and fixes https://savannah.gnu.org/bugs/?45573.
2 files changed