Camera: Fix AVFoundation provider to release the camera, start it async, and check if started before stopping it (#7303)

* Camera: Fix AVCamera to release the camera, start it async, and check if started before stopping it

* Camera: Additional check on storage.camera pre/post deinit

kivy/core/camera/camera_avfoundation.pyx

@@ -49,11 +49,20 @@ class CameraAVFoundation(CameraBase):
         self._framerate = 30
         super(CameraAVFoundation, self).__init__(**kwargs)
 
+    def __del__(self):
+        self._release_camera()
+
     def init_camera(self):
         cdef _AVStorage storage = <_AVStorage>self._storage
         storage.camera = avf_camera_init(
             self._index, self.resolution[0], self.resolution[1])
 
+    def _release_camera(self):
+        cdef _AVStorage storage = <_AVStorage>self._storage
+        if storage.camera != NULL:
+            avf_camera_deinit(storage.camera)
+            storage.camera = NULL
+
     @property
     def _scheduled_rate(self):
         # We're going 4 times faster the framerate to avoid frame skipping.

kivy/core/camera/camera_avfoundation_implem.m

@@ -214,7 +214,9 @@ Camera::Camera(int _cameraNum, int _width, int _height) {
 }
 
 Camera::~Camera() {
-    stopCaptureDevice();
+    if(started){
+        stopCaptureDevice();
+    }
 }
 
 bool Camera::grabFrame(double timeOut) {
@@ -411,7 +413,9 @@ int Camera::startCaptureDevice() {
 #endif
         [conn setVideoOrientation:default_orientation];
 
-        [mCaptureSession startRunning];
+        dispatch_async(dispatch_get_main_queue(), ^{
+            [mCaptureSession startRunning];
+        });
         [localpool drain];
 
         started = 1;