fix(path): check return value of append_path() (#28309)

If the filename passed to vim_FullName() is a relative directory, and
does not exist, it is appended to the current working directory. Since
the return value of append_path() was ignored, and if the buffer length
was too small to fit getcwd() + dirname(filename), it would still try to
append the basename(filename).

This was manifesting as a failure in test/unit/path_spec.lua in:
    itp('fails and uses filename if given filename contains non-existing directory', ..

This failure occurs when running the tests from directory with a short
path such as: /work/src/nv

    test/unit/path_spec.lua:420: Expected objects to be the same.
    Passed in:
    (string) '/work/src/nv/test.file'
    Expected:
    (string) 'non_existing_dir/test.file'

This return value for the second call to append_path() to append
basename(filename) was checked, and this is where it would fail for
normal / longer getcwd()s.

0 files changed, 0 insertions, 0 deletions