ALSA: Free global configuration tree after each snd_ctl_close and snd…

[mttjcksn]

In reference to issue #447:

This is a PR to update the ALSA backend to free the global configuration tree after each successful snd_*_open() (so actually after each snd_*_close()) in order to prevent memory leaks as described here.

To show the issue, valgrand memcheck was run on the test apps with following commands (RtAudio commit 7aba116):

valgrind --log-file=probe-mem.log --leak-check=full --show-leak-kinds=definite,indirect,possible --show-below-main=yes --dsymutil=no --leak-resolution=high --partial-loads-ok=no --track-origins=yes ./audioprobe
valgrind --log-file=record-mem.log --leak-check=full --show-leak-kinds=definite,indirect,possible --show-below-main=yes --dsymutil=no --leak-resolution=high --partial-loads-ok=no --track-origins=yes ./record 1 44100 8 0 0
valgrind --log-file=play-mem.log --leak-check=full --show-leak-kinds=definite,indirect,possible --show-below-main=yes --dsymutil=no --leak-resolution=high --partial-loads-ok=no --track-origins=yes ./playraw 1 44100 record.raw 0 0
valgrind --log-file=playsaw-mem.log --leak-check=full --show-leak-kinds=definite,indirect,possible --show-below-main=yes --dsymutil=no --leak-resolution=high --partial-loads-ok=no --track-origins=yes ./playsaw 2 48000 0 0 2
valgrind --log-file=testall-mem.log --leak-check=full --show-leak-kinds=definite,indirect,possible --show-below-main=yes --dsymutil=no --leak-resolution=high --partial-loads-ok=no --track-origins=yes ./testall 2 44100 0 0 0 0 
valgrind --log-file=teststops-mem.log --leak-check=full --show-leak-kinds=definite,indirect,possible --show-below-main=yes --dsymutil=no --leak-resolution=high --partial-loads-ok=no --track-origins=yes ./teststops 2 16000 0 0 0 0 

For all of these test apps, memcheck reports 118 errors, with 832 bytes definitely lost, 69,729 bytes possibly lost.

Following the patch, all report 0 erros and 0 bytes lost, except teststops, which reports 1 error of 768 bytes definitely lost. Perhaps another ALSA issue to investigate.

All pre and post-fix logs are attached. The post-fix logs are appended with -fork.
logs.zip