winegstreamer: Initialize COM on the callback dispatcher thread.

dlls/quartz/tests/filtergraph.c

@@ -760,7 +760,6 @@ static DWORD WINAPI call_RenderFile_multithread(LPVOID lParam)
     HRESULT hr;
 
     hr = IFilterGraph2_RenderFile(graph, filename, NULL);
-todo_wine
     ok(SUCCEEDED(hr), "RenderFile failed: %x\n", hr);
 
     if (SUCCEEDED(hr))

dlls/winegstreamer/gstdemux.c

@@ -2273,6 +2273,8 @@ static DWORD WINAPI dispatch_thread(void *user)
 {
     struct cb_data *cbdata;
 
+    CoInitializeEx(NULL, COINIT_MULTITHREADED);
+
     pthread_mutex_lock(&cb_list_lock);
 
     while(1){
@@ -2288,6 +2290,8 @@ static DWORD WINAPI dispatch_thread(void *user)
 
     pthread_mutex_unlock(&cb_list_lock);
 
+    CoUninitialize();
+
     return 0;
 }