copies-rust: move the mapping merging into a else clause
We are going to add more cases, to it is time to stop using early returns and to
move everything in a single if/elif/else block for clarity.
Differential Revision: https://phab.mercurial-scm.org/D9425
# 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