Lmms: Crash when copying audio TCOs between LMMSs.

[Sawuare]

Using Windows 10 Pro, 64-bit OS, x64-based processor with LMMS 1.2.0-rc.4.

To reproduce:

1. Open 2 LMMSs.
2. In each LMMS, add either a sample track or an AFP.
3. Add a TCO with info (not an empty sample track or AFP) to the track of a LMMS.
4. Control and drag the TCO from one LMMS's track to the other to make a copy.

Once the copied TCO enters the track, LMMS will crash, the runtime error window will appear,

then the "LMMS has stopped working" window will appear.

[musikBear]

Could not recreate exactly on win32. rc4 xp3
However, for* AFP *the actual TCO is stripped and only the instrument is copied to 2. instance of LMMS
Copying a 3oc track with TCO went perfect
Copying a sample-track track with TCO went perfect

[PhysSong]

Reproduced. It seems like TrackContentWidget::canPasteSelection assumes the source track is from the same instance of LMMS:
https://github.com/LMMS/lmms/blob/daa3f535158f321e7a01ea531fc3085f2d26ab37/src/core/Track.cpp#L1382-L1394

I guess saving track type in createTCODataFiles and using it in canPasteSelection will be enough.

[PhysSong]

Note that the crash only happens if a track whose index equals to the index of source track doesn't exist in target LMMS instance.

[PhysSong]

Should be fixed in #4862.