properly close the camera on pause

app/src/main/kotlin/com/simplemobiletools/camera/activities/MainActivity.kt

@@ -69,6 +69,7 @@ class MainActivity : SimpleActivity(), PreviewListener, PhotoProcessor.MediaSave
     override fun onResume() {
         super.onResume()
         if (hasStorageAndCameraPermissions()) {
+            mPreview?.onResumed()
             resumeCameraItems()
             setupPreviewImage(mIsInPhotoMode)
             scheduleFadeOut()
@@ -84,7 +85,6 @@ class MainActivity : SimpleActivity(), PreviewListener, PhotoProcessor.MediaSave
         if (hasStorageAndCameraPermissions()) {
             mOrientationEventListener.enable()
         }
-        mPreview?.onResumed()
     }
 
     override fun onPause() {

app/src/main/kotlin/com/simplemobiletools/camera/views/PreviewCameraTwo.kt

@@ -76,11 +76,8 @@ class PreviewCameraTwo : ViewGroup, TextureView.SurfaceTextureListener, MyPrevie
     }
 
     override fun onPaused() {
+        closeCamera()
         stopBackgroundThread()
-        mCaptureSession?.close()
-        mCameraDevice?.close()
-        mCameraDevice = null
-        mCaptureSession = null
     }
 
     override fun onSurfaceTextureSizeChanged(surface: SurfaceTexture?, width: Int, height: Int) {
@@ -125,6 +122,21 @@ class PreviewCameraTwo : ViewGroup, TextureView.SurfaceTextureListener, MyPrevie
         }
     }
 
+    private fun closeCamera() {
+        try {
+            mCameraOpenCloseLock.acquire()
+            mCaptureSession?.close()
+            mCaptureSession = null
+            mCameraDevice?.close()
+            mCameraDevice = null
+            mImageReader?.close()
+            mImageReader = null
+        } catch (e: Exception) {
+        } finally {
+            mCameraOpenCloseLock.release()
+        }
+    }
+
     private val imageAvailableListener = ImageReader.OnImageAvailableListener { reader ->
         val image = reader.acquireNextImage()
         val buffer = image.planes[0].buffer
@@ -249,7 +261,7 @@ class PreviewCameraTwo : ViewGroup, TextureView.SurfaceTextureListener, MyPrevie
         mTextureView.setTransform(matrix)
     }
 
-    private var cameraStateCallback = object : CameraDevice.StateCallback() {
+    private val cameraStateCallback = object : CameraDevice.StateCallback() {
         override fun onOpened(cameraDevice: CameraDevice) {
             mCameraOpenCloseLock.release()
             mCameraDevice = cameraDevice