Show error if camera could not be enabled.

Telegram/Resources/langs/lang.strings

@@ -2030,6 +2030,7 @@ https://github.com/telegramdesktop/tdesktop/blob/master/LEGAL
 "lng_group_call_chat_no_camera" = "You can't turn on video in this chat.";
 "lng_group_call_chat_no_screen" = "You can't share your screen in this chat.";
 "lng_group_call_failed_screen" = "An error occured. Screencast has stopped.";
+"lng_group_call_failed_camera" = "Could not enable camera. Perhaps another app is using the camera already. Try closing other apps.";
 "lng_group_call_tooltip_screen" = "Share screen";
 "lng_group_call_tooltip_camera" = "Your camera is off. Click here to enable camera.";
 "lng_group_call_tooltip_microphone" = "You are on mute. Click here to speak.";

Telegram/SourceFiles/calls/group/calls_group_call.cpp

@@ -1989,6 +1989,10 @@ bool GroupCall::emitShareCameraError() {
 
 void GroupCall::emitShareCameraError(Error error) {
 	_cameraState = Webrtc::VideoState::Inactive;
+	if (error == Error::CameraFailed
+		&& Webrtc::GetVideoInputList().empty()) {
+		error = Error::NoCamera;
+	}
 	_errors.fire_copy(error);
 }
 
@@ -2042,8 +2046,14 @@ void GroupCall::setupOutgoingVideo() {
 				_cameraCapture = _delegate->groupCallGetVideoCapture(
 					_cameraInputId);
 				if (!_cameraCapture) {
-					return emitShareCameraError(Error::NoCamera);
+					return emitShareCameraError(Error::CameraFailed);
 				}
+				const auto weak = base::make_weak(this);
+				_cameraCapture->setOnFatalError([=] {
+					crl::on_main(weak, [=] {
+						emitShareCameraError(Error::CameraFailed);
+					});
+				});
 			} else {
 				_cameraCapture->switchToDevice(_cameraInputId.toStdString());
 			}

Telegram/SourceFiles/calls/group/calls_group_common.h

@@ -61,6 +61,7 @@ enum class VideoQuality {
 
 enum class Error {
 	NoCamera,
+	CameraFailed,
 	ScreenFailed,
 	MutedNoCamera,
 	MutedNoScreen,

Telegram/SourceFiles/calls/group/calls_group_toasts.cpp

@@ -155,6 +155,8 @@ void Toasts::setupError() {
 		const auto key = [&] {
 			switch (error) {
 			case Error::NoCamera: return tr::lng_call_error_no_camera;
+			case Error::CameraFailed:
+				return tr::lng_group_call_failed_camera;
 			case Error::ScreenFailed:
 				return tr::lng_group_call_failed_screen;
 			case Error::MutedNoCamera: