Description
I clicked on "ctrl"+"↓" when selecting a string with a note on another string.

To Reproduce

1. Open Power Tab Editor.
2. Press "ctrl"+"N" to create new file.
3. Press "↓" to locate the note, then press "0" to create it:
   
4. Press "↑" to change string:
   
5. Press "ctrl"+"↓" to crash:
   
6. Click "Report Bug..."
7. Submit new issue.

Additional Info
Segmentation fault 0# 0x00007FF67CE67208 in powertabeditor
1# 0x00007FF67CE6643B in powertabeditor
2# 0x00007FF67CE67B6F in powertabeditor
3# seh_filter_exe in ucrtbase
4# 0x00007FF67D023F19 in powertabeditor
5# _C_specific_handler in VCRUNTIME140
6# _chkstk in ntdll
7# RtlRaiseException in ntdll
8# KiUserExceptionDispatcher in ntdll
9# 0x00007FF67CFCCC76 in powertabeditor
10# 0x00007FF67CF0A25E in powertabeditor
11# 0x00007FF67CF0A1B5 in powertabeditor
12# QUndoStack::push in Qt5Widgets
13# 0x00007FF67CF0AEF0 in powertabeditor
14# 0x00007FF67CE910E1 in powertabeditor
15# QObject::qt_static_metacall in Qt5Core
16# QAction::activate in Qt5Widgets
17# QAction::event in Qt5Widgets
18# QApplicationPrivate::notify_helper in Qt5Widgets
19# QApplication::notify in Qt5Widgets
20# QCoreApplication::notifyInternal2 in Qt5Core
21# QShortcutMap::dispatchEvent in Qt5Gui
22# QShortcutMap::tryShortcut in Qt5Gui
23# QWindowSystemInterface::handleShortcutEvent in Qt5Gui
24# QGuiApplicationPrivate::processKeyEvent in Qt5Gui
25# QWindowSystemInterface::sendWindowSystemEvents in Qt5Gui
26# QEventDispatcherWin32::processEvents in Qt5Core
27# qt_plugin_query_metadata in qwindows
28# QEventLoop::exec in Qt5Core
29# QCoreApplication::exec in Qt5Core
30# 0x00007FF67CE68D66 in powertabeditor
31# 0x00007FF67D00A187 in powertabeditor
32# 0x00007FF67D0088CA in powertabeditor
33# BaseThreadInitThunk in KERNEL32
34# RtlUserThreadStart in ntdll

Version
Windows 10 21H2
Power Tab Editor 2.0 Beta (v2.0.0-alpha18-0-g1f2771b2)