Clear self.pending_whitespace.max_content in forced_line_break()
If we encountered a preserved line break after some whitespace, we were
including the space in the max-content size of the following line.
So just like line_break_opportunity() was already clearing
self.pending_whitespace.min_content, forced_line_break() needs to
clear self.pending_whitespace.max_content too.
Also some cosmetic refactoring.
Signed-off-by: Oriol Brufau obrufau@igalia.com