handle none type doc order

[sildater]

(reopen PR to correct branch)

The current matchfile_from_alignment from alignment uses the document order of notes in line 361 (exportmatch,py)

snote_sort_info[snote.id] = (onset_beats, snote.doc_order)

to later on sort by this value in line 460 ff

sort_stime = np.array(sort_stime)
sort_stime_idx = np.lexsort((sort_stime[:, 1], sort_stime[:, 0]))
note_lines = np.array(note_lines)[sort_stime_idx]

doc_order is a standard note property but it's only used for musicxml files so far. Scores/parts imported from match/mei/kern/midi do not have this property and the sorting breaks. A doc_order property shouldn't be a hard requirement though, so the doc_order extraction is now:

snote_sort_info[snote.id] = (onset_beats, snote.doc_order if snote.doc_order is not None else 0)

[codecov-commenter]

Codecov Report

Attention: 19 lines in your changes are missing coverage. Please review.

Files	Coverage Δ
partitura/io/__init__.py	81.53% <100.00%> (ø)
partitura/io/exportmatch.py	79.79% <100.00%> (ø)
partitura/io/importkern.py	85.36% <ø> (+0.21%)	:arrow_up:
partitura/io/importmidi.py	87.50% <100.00%> (ø)
partitura/io/importnakamura.py	85.71% <100.00%> (ø)
tests/test_tonal_tension.py	100.00% <ø> (ø)
partitura/io/musescore.py	41.93% <0.00%> (+14.46%)	:arrow_up:
tests/test_musescore.py	75.00% <45.45%> (-25.00%)	:arrow_down:
partitura/performance.py	84.97% <84.28%> (+5.97%)	:arrow_up:

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