Fix some cppcheck reports

There are still these (if we exclude the cppcheck reports pointing on src-old):
[src/libmidi/midi_event.h:61]: (warning) Member variable 'MidiEvent::deltaPulses' is not initialized in the constructor.
[src/libmidi/midi_event.h:61]: (warning) Member variable 'MidiEvent::metaType' is not initialized in the constructor.
[src/screens/one_player_screen/note_ground.cpp:21]: (warning) Member variable 'NoteGround::microSecondPerPixel' is not initialized in the constructor.
but perhaps it's on purpose.