multimedia/qmmp-qt5: update to 1.7.6 release (+)

Changes since 1.7.5:

• using system scroll settings for playlists;
• using stable order for keys in the playlists.txt file;
• added support for float PCM format in the dsound and wasapi plugins;
• fixed seeking from command-line;
• fixed support for special keys in the shortcut editor dialog;
• fixed track index calculation;
• fixed possible crash in the library plugin;
• fixed compatibility with Qt 5.12;
• fixed Chinese Traditional translation.