Fix crash for picture callback after stop()

The callback is using the captured camera object instead of checking the
mCamera object to verify that we haven't released yet. Also, added a getter
for the flash property.

camerakit/src/main/api16/com/flurgle/camerakit/Camera1.java

@@ -214,7 +214,9 @@ public class Camera1 extends CameraImpl {
                     @Override
                     public void onPictureTaken(byte[] data, Camera camera) {
                         mCameraListener.onPictureTaken(data);
-                        camera.startPreview();
+                        if (mCamera != null) {
+                            mCamera.startPreview();
+                        }
                     }
                 });
                 break;

camerakit/src/main/java/com/flurgle/camerakit/CameraView.java

@@ -330,6 +330,11 @@ public class CameraView extends FrameLayout implements LifecycleObserver {
         mCameraImpl.setFlash(flash);
     }
 
+    @Flash
+    public int getFlash() {
+        return mFlash;
+    }
+
     public void setFocus(@Focus int focus) {
         this.mFocus = focus;
         if (this.mFocus == CameraKit.Constants.FOCUS_TAP_WITH_MARKER) {