multimedia/mlt7: Backport bugfixes

Backport upstream commit a3d49ccb92e2544bcc1957ce046bf63f71b468a6 to
fix crackling FLAC audio and 1eee2187410ae16f520409dcdcf6de789d8bafd9
for potential build issues with FFmpeg 6 which should fix build
on -CURRENT

References:
https://github.com/mltframework/mlt/commit/a3d49ccb92e2544bcc1957ce046bf63f71b468a6
https://github.com/mltframework/mlt/commit/1eee2187410ae16f520409dcdcf6de789d8bafd9

PR:		271161
Approved by:	kde (tcberner via IRC)
Sponsored by:	Blinkinblox