memblockq: Adjust tail chunk offset into memblock after split
requested to merge igor.v.kovalenko/pulseaudio:pr/issue-3789-memblockq-write-tail-chunk-wrong-offset into master
If pa_memblockq_push needs to write into the middle of a chunk, target chunk is split into head and tail sharing the same memblock. Size of head and tail chunks is adjusted correctly, head chunk pointer into memblock remains unchanged from target chunk.
The problem is with tail chunk offset into memblock which should be advanced past write region of memblock, but currently it is left as 0.
This is causing an issue where seeking a few frames back into the middle of memblock and writing a frame there ends up with tail chunk referencing frames from very beginning of memblock causing corrupted output from memblockq.
Fix this by adjusting tail chunk offset into memblock past write region and add a test case.
Fixes #3789 (closed)