ambient_depth_filter_editor is not ignoring 'SVN_ERR_WC_PATH_NOT_FOUND' errors.

Hi All,

Prabhu got stuck with his upcoming default 'send-copy-args=True' work
for his diff enhancements.

Basically he got diff-tests-44 to fail due to
"ambient_depth_filter_editor is *not* ignoring
'SVN_ERR_WC_PATH_NOT_FOUND' errors."

I could see many other callers ignoring the errors
'SVN_ERR_WC_PATH_NOT_FOUND' especially when it is returned by
svn_wc__db_read_info(Ex subversion/libsvn_wc/diff.c:close_file).

I guess ambient_depth_filter_editor's close_file can also behave like
others.

I lack a context to justify this fix, here right now.

I am yet to run full testsuite, I ran only diff_tests with this patch
and Prabhu's patch it passes.

Any thoughts?

With regards
Kamesh Jayachandran