fix(virtual-backgrounds) fix error if we failed to load the model

If another try is made, show an error notification instead of failing with an
exception.

react/features/stream-effects/virtual-background/index.js

 
             return;
         }
+    } else if (isWasmDisabled) {
+        dispatch(showWarningNotification({
+            titleKey: 'virtualBackground.backgroundEffectError'
+        }, NOTIFICATION_TIMEOUT_TYPE.LONG));
+
+        return;
     }
 
     const modelBufferOffset = tflite._getModelBufferMemoryOffset();