Fix bug where pattern header was sometimes not redrawn

[nyanpasu64]

In 0.5.0 and before, pressing Shift+Tab repeatedly until you reach FM 2 will fail to redraw the header, because oldLeftTrackIdx was erroneously declared a bool.

In builds since accb5ac (accb5ac#diff-97d96a2c599e40b88ae7e016d1b61a16bbb5cb81d4ef24f08c83fa5e8f2307fb) (more recent than 0.5.0), placing the cursor in the leftmost column, then pressing Shift+Tab to jump to the right an even number of columns, will fail to redraw the header, and 1 of every 2 subsequent Shift+Tab presses will fail to redraw. This is due to the bizarre static_cast<bool>(leftTrackVisIdx_&1) != oldLeftTrackIdx comparison.

This fixes both problems by declaring oldLeftTrackIdx as an int, and comparing it to leftTrackVisIdx_ directly.

[nyanpasu64]

not waiting for CI to pass is... brave.

[OPNA2608]

Yes.