Fix Exception for calling stop in onPictureTaken Callback

Fixes bug #67

Author: bsagal

library/src/main/api14/com/google/android/cameraview/Camera1.java

@@ -243,6 +243,7 @@ void takePictureInternal() {
                 public void onPictureTaken(byte[] data, Camera camera) {
                     isPictureCaptureInProgress.set(false);
                     mCallback.onPictureTaken(data);
+                    if (!isCameraOpened()) return;
                     camera.cancelAutoFocus();
                     camera.startPreview();
                 }

library/src/main/api21/com/google/android/cameraview/Camera2.java

@@ -650,6 +650,7 @@ public void onCaptureCompleted(@NonNull CameraCaptureSession session,
      * capturing a still picture.
      */
     void unlockFocus() {
+        if (!isCameraOpened()) return;
         mPreviewRequestBuilder.set(CaptureRequest.CONTROL_AF_TRIGGER,
                 CaptureRequest.CONTROL_AF_TRIGGER_CANCEL);
         try {