linux: set playback rate and set volume not working

[esiqveland]

When running the example I noticed only volume set to max (1.0) works. everything < 1.0 gets used as zero volume. Noticed the same for playback rate.

I tracked it down to std::to_string being locale aware, and in my locale it prints a float with comma , as the decimal point, breaking the volume setting.

https://github.com/harmonoid/libwinmedia/blob/master/linux/player.hpp#L410