lib: fix volume range check in libvlc_audio_set_volume()
lib: fix (pre)amplification range checks for equalizer
lib: return NAN on libvlc_audio_equalizer_set_amp_at_index() error
lib: do not convert to double in libvlc_video_set_scale()
lib: check scale range in libvlc_video_set_scale()
lib: fix logic inversion
qt4: fix memory leak
float: fix copy-paste error in double precision amp