style files (MSS) that list name of chord description file do not take effect on load

First discovered in a self-built binary on Windows, but verified using a7e207d - a nightly from shortly before I made my branches.

1) load attached score uses_cchords_muse.mscx
2) verify chords render as "Cma7" and "Cmi7"
3) load the attached style file sym_description_only.mss

Expected result: chords change to render using triangle and dash.
Actual result: no change to rendering

This happens because the style file contains only a reference to the chord description file, and does not contain the full embedded information, and the code that loads style files does not actually bother loading the chord description file listed in the style file. Style files created in 1.X will only list the name of the chord description file, so this basically means 1.X style files won't work as is if they are trying to load a different chord description file.

We could fix this so that loading a style file does load a listed chord description file (probably only if there is no embedded chord information as well). Or we could say that we don't support 1.X style files, or special case 1.X style files.