sink: prevent DecodingStopped signal if not started

Arbitrate DRing::VideoSignal::DecodingStopped signal to not
emitting it if not previously started.
This prevents client troubles if they don't handle well
this behavior.

Issue: #81116
Change-Id: Ib08801d2f62795550238bc91810e6bf139376553

src/media/video/sinkclient.cpp

@@ -353,10 +353,12 @@ SinkClient::setFrameSize(int width, int height)
         RING_WARN("Start sink <%s / %s>, size=%dx%d, mixer=%u",
                  getId().c_str(), openedName().c_str(), width, height, mixer_);
         emitSignal<DRing::VideoSignal::DecodingStarted>(getId(), openedName(), width, height, mixer_);
-    } else {
+        started_ = true;
+    } else if (started_) {
         RING_ERR("Stop sink <%s / %s>, mixer=%u",
                  getId().c_str(), openedName().c_str(), mixer_);
         emitSignal<DRing::VideoSignal::DecodingStopped>(getId(), openedName(), mixer_);
+        started_ = false;
     }
 }
 

src/media/video/sinkclient.h

@@ -65,6 +65,7 @@ class SinkClient : public VideoFramePassiveReader
     private:
         const std::string id_;
         const bool mixer_;
+        bool started_ {false}; // used to arbitrate client's stop signal.
         std::function<void(int, int)> target_;
         std::vector<unsigned char>* targetData_ {nullptr}; // filled by registerTarget, user owned