LPCM: fix 20/24-bit decoding

Fixes: #9907
Qt: correctly update the art URL
lpcm bd: fix decoding of 16 bits with channels padding

swab prototype is not the same as memcpy (src and dst are swapped)
Fixed warnings on duplicate const modifiers.

Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>
Fixed warning on assignment as a condition without parentheses.

Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>