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.