dshow: check CoInitialize() in callbacks

If the calling thread is using COM with MTA model, then CoInitializeEx()
will fail, and CoUninitialize() will be unbalanced. Ultimately, the
calling thread is likely to crash. (CoInitializeEx() could also fail in
case of memory error, but that is unlikely).

modules/access/dshow/dshow.cpp

@@ -2013,18 +2013,15 @@ static int DemuxControl( demux_t *p_demux, int i_query, va_list args )
 static int FindDevices( vlc_object_t *p_this, const char *psz_name,
                             char ***vp, char ***tp )
 {
-    bool b_audio = !strcmp( psz_name, CFG_PREFIX "adev" );
-
     /* Find list of devices */
     list<string> list_devices;
-
-    /* Initialize OLE/COM */
-    CoInitializeEx( NULL, COINIT_APARTMENTTHREADED );
+    if( SUCCEEDED(CoInitializeEx( NULL, COINIT_APARTMENTTHREADED )) )
+    {
+        bool b_audio = !strcmp( psz_name, CFG_PREFIX "adev" );
 
         FindCaptureDevice( p_this, NULL, &list_devices, b_audio );
-
-    /* Uninitialize OLE/COM */
         CoUninitialize();
+    }
 
     unsigned count = 2 + list_devices.size(), i = 2;
     char **values = (char **)xmalloc( count * sizeof(*values) );
@@ -2058,11 +2055,12 @@ static int ConfigDevicesCallback( vlc_object_t *p_this, char const *psz_name,
     char *psz_device = NULL;
     int i_ret = VLC_SUCCESS;
 
+    if( FAILED(CoInitializeEx( NULL, COINIT_APARTMENTTHREADED )) )
+        return VLC_EGENERIC;
+
     if( !EMPTY_STR( newval.psz_string ) )
         psz_device = strdup( newval.psz_string );
 
-    /* Initialize OLE/COM */
-    CoInitializeEx( NULL, COINIT_APARTMENTTHREADED );
 
     p_item = config_FindConfig( p_this, psz_name );
 
@@ -2109,9 +2107,7 @@ static int ConfigDevicesCallback( vlc_object_t *p_this, char const *psz_name,
         i_ret = VLC_EGENERIC;
     }
 
-    /* Uninitialize OLE/COM */
     CoUninitialize();
-
     free( psz_device );
     return i_ret;
 }