Initially thew new region has a length of zero (0:0). When
merging Notes from a truncated region (no explicit note-off)
those notes are lost:
"Stuck note resolution - end time @ 0:0 is before note on: @ 0:0"
Truncate (or split) a region so that a note is cut short:
```
Region [{<--Note-------->}]
```
becomes
```
Region [{<--Note--]
^ implicit note-off at region boundary
```
When combining this region with an empty Region after gap,
```
Region [{<--Note--] [ ]
```
the result should be
```
Region [{<--Note->} ]
```
For this reason, even without a gap between the regions,
the original note length must not be restored.
The result MUST NOT be the same as the original:
```
Region [{<--Note-------->}]
```
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