Disappearing tempo/system text when hiding empty staves
Both tempo text and system text are disappearing when hiding empty staves and the top-most staff is empty.
Steps to reproduce:
1. Open attached score.
2. Activate "Hide empty staves" option.
The tempo text and the system text in the second system are disappearing. Also it seems that the system text is treated as staff text of the top-most staff (it was produced as system text via Ctrl-Shift-T while the first note of the measure in the viola staff was selected). If you right-click it, it shows "staff text", not "system text".