Fix ui glitch where track ticks did not line up

[enp2s0]

This fixes the a bug (see #4155) where the instrument-track ticks did not line up with the timeline. This only applies to stable-1.2. A different fix would be required to fix master, the code is completely different.

[BaraMGB]

Can you explain what's the difference between fixing stable and master?

[enp2s0]

@BaraMGB they're different branches. stable-1.2 is a stable release and is only accepting bug fixes and not new features (to prevent code from breaking), master is the bleeding edge development version and is the most up-to-date (but sometimes has new bugs). Because stable and master had different code for the bug I was fixing, my for only worked in stable and not master.

[zonkmachine]

Because stable and master had different code for the bug I was fixing,

I think this was the question. What has changed between stable-1.2 and master?
Here is the output of git diff stable-1.2 master -- src/tracks/Pattern.cpp

The changes in this PR touches code here that needs some 'lovin' in order to be mergeable into master.

[zonkmachine]

Merge? (We merge this now and keep #4155 open for a final fix in master.)

[zonkmachine]

I believe this line in master is the equivalent of the line that's changed in this PR.

lmms/src/tracks/Pattern.cpp

Line 904 in 56b4740

const float pixelsPerTact = ( baseWidth - 2 * TCO_BORDER_WIDTH ) / (float) m_pat->length().getTact();

Merging.