Score file reading: fix bar line span for non-5-line staves.

While reading a score, if a staff is found with number of lines != 5 and no explicit bar line span set (i.e. default bar line span), the bar line span remains set as for a 5-line staff.
Merge pull request #909 from mgavioli/fix_reading_bar_line_span_for_non5line_staves

Fix score file reading: bar line span for non-5-line staves.