multimedia/qmmp-qt6: update to 2.1.5 release (+)

Changes since 2.1.4:
* added waveform seekbar optimization;
* fixed visualization initialization in the simple user interface;
* fixed playlist geometry issues in the simple user interface;
* fixed playlist settings in the skinned user interface;
* fixed possible crash;
* fixed http version;
* fixed file type determination by content in the waveform seekbar.