dirstate: fix compilation warnings in `dirstate_item_set_possibly_dirty()`
Since https://phab.mercurial-scm.org/D11387 (i.e. the same patch as
mentioned in my previous patch), Clang has also started warning about
`dirstate_item_set_possibly_dirty()` missing an explicit return, and
about its use of the result of an assignment as a condition without
using parentheses. This patch fixes that.
Differential Revision: https://phab.mercurial-scm.org/D11445
# Files that just need to be migrated to the formatter.
# Do not add new files here!
mercurial/cext/manifest.c
mercurial/cext/osutil.c
# Vendored code that we should never format:
syntax: glob
contrib/python-zstandard/**.c
contrib/python-zstandard/**.h
hgext/fsmonitor/pywatchman/**.c
mercurial/thirdparty/**.c
mercurial/thirdparty/**.h
mercurial/pythoncapi_compat.h