Memory corruption happened to the media frame caches when an audio hook
freed a frame when it shouldn't.  I think the freed frame was because a
jitter buffer interpolated a missing frame and the audio hook
unconditionally freed it.

* Made audiohook.c:audio_audiohook_write_list() not free an interpolated
frame if it is the same frame as what was passed into the routine.

* Made plc.c:normalise_history() use memmove() instead of memcpy() on a
memory block that could overlap.  Found by valgrind investigating this
issue.

ASTERISK-27238
ASTERISK-27412

Change-Id: I548d86894281fc4529aefeb9f161f2131ecc6fde