SampleBuffer: fix a segfault when moving a loop point while playing a note, also do some sptring cleanup (some unused/redundant variables removed)
Also, some codepath optimization: add a method to SampleBuffer for setting all loop/start/endpoints at once, so we don't have to wait for mutex unlocks 4 times in a row. Then make AFP utilize this method.
Merge pull request #559 from diizy/loops

SampleBuffer: fix a segfault when moving a loop point while playing a no...