This fixes a crash with missing [MIDI] write-sources after
duplicating tracks [1]: Stealing write-source name fails, because
there is no write-source.
When duplicating tracks, reset_write_sources() is called before
any playlists are set [2]. So no new write-sources are created
because _playlists[DATA-TYPE] is empty.
During normal track creation write-sources are usually added
by the input-change handler [3]. However in this case the
state has been set, and since there is no change,
DiskWriter::configure_io does not call use_new_write_source()
NB. This also re-creates write-source when playlists are changed.
-=-
[1]
#3 0x00007f4420690102 in __GI___assert_fail at assert.c:101
#4 0x0000562bfa300dc9 in boost::shared_ptr<ARDOUR::SMFSource>::operator->() const at /usr/include/boost/smart_ptr/shared_ptr.hpp:734
#5 0x00007f442579ffa1 in ARDOUR::DiskWriter::steal_write_source_name[abi:cxx11]() at ../libs/ardour/disk_writer.cc:1290
#6 0x00007f4425e476b6 in ARDOUR::Track::steal_write_source_name[abi:cxx11]() at ../libs/ardour/track.cc:476
#7 0x00007f4425d060a2 in ARDOUR::Session::create_midi_source_by_stealing_name at ../libs/ardour/session.cc:4955
#8 0x0000562bf9ed39ab in MidiTimeAxisView::add_region at ../gtk2_ardour/midi_time_axis.cc:1650
#9 0x0000562bf9b05f2a in Drag::add_midi_region at ../gtk2_ardour/editor_drag.cc:568
-=-
[2]
#0 0x00007ffff7582e2f in ARDOUR::DiskWriter::reset_write_sources at ../libs/ardour/disk_writer.cc:946
#1 0x00007ffff757fce6 in ARDOUR::DiskWriter::set_state at ../libs/ardour/disk_writer.cc:333
#2 0x00007ffff7a81c93 in ARDOUR::Route::set_processor_state at ../libs/ardour/route.cc:3054
#3 0x00007ffff7a7f5d5 in ARDOUR::Route::set_state at ../libs/ardour/route.cc:2697
#4 0x00007ffff7c2aa1d in ARDOUR::Track::set_state at ../libs/ardour/track.cc:172
#5 0x00007ffff794f204 in ARDOUR::MidiTrack::set_state at ../libs/ardour/midi_track.cc:152
#6 0x00007ffff7b7e06b in ARDOUR::Session::XMLRouteFactory at ../libs/ardour/session_state.cc:1890
#7 0x00007ffff7addf7e in ARDOUR::Session::new_route_from_template at ../libs/ardour/session.cc:3048
#8 0x000055555621329a in DuplicateRouteDialog::on_response(int) at ../gtk2_ardour/duplicate_routes_dialog.cc:194
-=-
[3]
#0 0x00007ffff7583243 in ARDOUR::DiskWriter::use_new_write_source at ../libs/ardour/disk_writer.cc:996
#1 0x00007ffff75831c7 in ARDOUR::DiskWriter::reset_write_sources at ../libs/ardour/disk_writer.cc:989
#2 0x00007ffff75851ea in ARDOUR::DiskWriter::configure_io at ../libs/ardour/disk_writer.cc:1335
#3 0x00007ffff7a7b308 in ARDOUR::Route::configure_processors_unlocked at ../libs/ardour/route.cc:1912
#4 0x00007ffff7a79e4b in ARDOUR::Route::configure_processors at ../libs/ardour/route.cc:1719
#5 0x00007ffff7a86695 in ARDOUR::Route::input_change_handler at ../libs/ardour/route.cc:3632
b279c42158