Allow backends to work without stepping when threading is disabled.

This is per-backend.

miniaudio.h

@@ -7297,6 +7297,7 @@ typedef struct ma_device_backend_info
     const char* pName;
     ma_bool32 isLoopbackSupported;
     ma_bool32 noAudioThread;    /* When set to true, the backend does not create a miniaudio-managed audio thread. Will be used for backends like Web Audio, or those that run on platforms that do not support multithreading. Depending on the backend, this may force single-threaded mode. Single-threaded mode will not be enforced for the Web Audio backend. */
+    ma_bool32 isMultiThreadedModeAllowedWhenThreadingDisabled;  /* When set to true, the backend must be 100% thread safe. */
 } ma_device_backend_info;
 
 
@@ -45937,6 +45938,7 @@ static void ma_backend_info__webaudio(ma_device_backend_info* pBackendInfo)
     MA_ASSERT(pBackendInfo != NULL);
     pBackendInfo->pName = "Web Audio";
     pBackendInfo->noAudioThread = MA_TRUE;  /* We don't want to be creating a miniaudio-managed audio thread with Web Audio. */
+    pBackendInfo->isMultiThreadedModeAllowedWhenThreadingDisabled = MA_TRUE;
 }
 
 static ma_result ma_context_init__webaudio(ma_context* pContext, const void* pContextBackendConfig, void** ppContextState)
@@ -48428,18 +48430,20 @@ MA_API ma_result ma_device_init(ma_context* pContext, const ma_device_config* pC
         return MA_INVALID_ARGS;
     }
 
+    /* We'll need the backend info to determine whether or not an audio thread can be created. */
+    ma_context_get_backend_info(pContext, &backendInfo);
+
     threadingMode = pConfig->threadingMode;
 
     /* Force single-threaded mode if threading has been disabled at compile time. */
     #ifdef MA_NO_THREADING
     {
+        if (!backendInfo.isMultiThreadedModeAllowedWhenThreadingDisabled) {
             threadingMode = MA_THREADING_MODE_SINGLE_THREADED;
         }
+    }
     #endif
 
-    /* We'll need the backend info to determine whether or not an audio thread can be created. */
-    ma_context_get_backend_info(pContext, &backendInfo);
-
     /* Check that we have our callbacks defined. */
     if (pContext->pVTable->onDeviceInit == NULL) {
         return MA_INVALID_OPERATION;