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-------->}]
```
Playlist::split can result in removal of a region
(adding two others instead). In this case the state
of the removed region (if modified) is not saved.
I/O plugin Controls are destroyed with ~IOPlug, however
Session::destroy()'s call to drop_references() still
triggers AutomationControl::session_going_away() on the
binding proxy.
This is even properly documented in session_object.h:
> A named object associated with a Session. Objects derived
> from this class are expected to be destroyed before the
> session calls drop_references().
Playlist::add_region, Playlist::add_region_internal always
adds the region to the top of the playlist, ignoring the
region's layer.
Note that there is also difference between
Region::layer and Region::layering_index.
Previously creating a new preset first attempted to load
it from disk, before creating it. This resulted in a
`XML error: failed to load external entity`.
The definitions from <stdatomic.h> conflict with <atomic>, which causes
a build failure since <atomic> is included previously.
Signed-off-by: Violet Purcell <vimproved@inventati.org>
