Bug: Adding output directory breaks form output paths

[KeyWorksRW]

Description:

When a project's language output directory is set when previously empty, all the forms get modified to prefix their files with the output directory, which results in errors when generating the files.

• Example: assume prop_base_directory is empty and prop_base_file for a form is "bar".

• Change: prop_base_directory to "foo".

• Result: prop_base_file is now "foo/bar" which will try to generate "foo/foo/bar.cpp"

• Expected: either prop_base_file should not have changed at all, or it should have changed to "../bar" to generate the file in the original location.