ma_slot_allocator_free: use atomic load on allocator count

Signed-off-by: Steven Noonan <steven@uplinklabs.net>

miniaudio.h

@@ -38986,7 +38986,7 @@ MA_API ma_result ma_slot_allocator_free(ma_slot_allocator* pAllocator, ma_uint64
 
     MA_ASSERT(iBit < 32);   /* This must be true due to the logic we used to actually calculate it. */
 
-    while (pAllocator->count > 0) {
+    while (c89atomic_load_i32(&pAllocator->count) > 0) {
         /* CAS */
         ma_uint32 oldBitfield;
         ma_uint32 newBitfield;