Fix frash in uninitialized driver_format.matrix.

Thread 1 "zsnes" received signal SIGSEGV, Segmentation fault.
__strlen_sse2_bsf () at ../sysdeps/i386/i686/multiarch/strlen-sse2-bsf.S:50
50      ../sysdeps/i386/i686/multiarch/strlen-sse2-bsf.S: Нет такого файла или каталога.
(gdb) bt
#0  __strlen_sse2_bsf () at ../sysdeps/i386/i686/multiarch/strlen-sse2-bsf.S:50
#1  0xf7e3c491 in _sanitize_matrix (maxchannels=2, matrix=0x1c00200 <error: Cannot access memory at address 0x1c00200>, device=device@entry=0x57057100)
    at ../../libao-1.2.2/src/audio_out.c:634
#2  0xf7e3e9bc in _open_device (driver_id=<optimized out>, format=format@entry=0xffffc638, options=options@entry=0x0, file=0x0) at ../../libao-1.2.2/src/audio_out.c:991
#3  0xf7e3f579 in ao_open_live (driver_id=<optimized out>, format=0xffffc638, options=0x0) at ../../libao-1.2.2/src/audio_out.c:1337
#4  0x5699fbb5 in SoundInit_ao () at linux/audio.c:197
#5  InitSound () at linux/audio.c:338
#6  0x569a2f7f in initwinvideo () at linux/sdllink.c:1080
#7  0x569a07d3 in initvideo ()
#8  0x56ad59bc in regptwa ()
#9  0x56a3c490 in SA1tableG ()
#10 0xffffc808 in ?? ()
#11 0xf78619b5 in __libc_start_main (main=0x1, argc=1450015920, argv=0x0, init=0x566d7ce1 <_start+49>, fini=0x566d7c00 <main>, rtld_fini=0x1, stack_end=0xffffc8c4) at ../csu/libc-start.c:332
#12 0x569cd000 in ?? ()
--- a/linux/audio.c
+++ b/linux/audio.c
@@ -166,6 +166,7 @@ static int SoundInit_ao()
   if (driver_id < 0) { driver_id = ao_default_driver_id(); }
 
   ao_sample_format driver_format;
+  memset(&driver_format, 0, sizeof(driver_format));
   driver_format.bits = 16;
   driver_format.channels = StereoSound+1;
   driver_format.rate = freqtab[SoundQuality = ((SoundQuality > 6) ? 1 : SoundQuality)];