MPV: Fix the MPV controls

By default, don't create and initialize the MPV context, do it when the user request to play the video. This is done to not rely on race condition between the window creation and the MPV lib trying to get the window ID.

src/UI/DocumentViews/MpvContainer.cc

@@ -297,6 +297,10 @@ MpvContainer::mpvPause() noexcept
 void
 MpvContainer::mpvTogglePlayback() noexcept
 {
+    if (!isMpvAlreadyInitialized) {
+        reCreateMpvContext();
+    }
+
     logDebug() << "MPV: Toggling the playback";
     asyncCommand(AsyncCmdType::TogglePlayback, { "cycle", "pause", "up", nullptr });
 }