fix: change at eof

[psteinroe]

trying to fix a bug where all statements are deleted when deleting at eof. and when modifying a statement.

fixes:

• using line index of old document during change instead of new
• gracefully handling changes that are out of bounds of the current content. no idea why these are sent, but they are sometimes. instead of investigating where they come from I just added a check to ensure a TextRange is always valid.
• change_range in ModifiedStatement was not adapted to the range of the statement, causing a crash and invalid diagnostics ranges when modifying within a statement.