nodemap: deal with data mmap error
If the file is too small, the mmapread call would raise a ValueError. We catch
that and ignore nodemap content (as we do without mmap). This make the repository
slightly slower (until the next write) but usable. Unlike the current crash.
Differential Revision: https://phab.mercurial-scm.org/D10458
edition = "2018"
max_width = 79
wrap_comments = true
error_on_line_overflow = true