VAAPI: Add workaround for 'via' VDPAU drivers: do not block on closing vaapi context.

The code blocks in libva vaSyncSurface() when the decoding context has been destroyed.
The problem is observed with a 'via' vdpau driver.

modules/codec/avcodec/va.c

@@ -179,6 +179,11 @@ static void destroy_surfaces( vlc_va_conn_t *conn )
     if( conn->i_ref_count > 1 )
         return;
 
+    bool b_workaround = false;
+    const char *psz_driver = getenv("VDPAU_DRIVER");
+    if( psz_driver && (strcmp(psz_driver, "via") == 0) )
+        b_workaround = true;
+
     for( unsigned int i = 0; i < conn->pool.count; i++ )
     {
         vlc_va_surface_t *surface = &conn->pool.p_surfaces[i];
@@ -187,11 +192,13 @@ static void destroy_surfaces( vlc_va_conn_t *conn )
         if( surface->i_refcount > 1 )
             abort();
 
+        if( !b_workaround &&
 #if VA_CHECK_VERSION(0,31,0)
-        if( vaSyncSurface( conn->p_display, surface->i_id ) )
+            vaSyncSurface( conn->p_display, surface->i_id )
 #else
-        if( vaSyncSurface( conn->p_display, conn->i_context_id, surface->i_id ) )
+            vaSyncSurface( conn->p_display, conn->i_context_id, surface->i_id )
 #endif
+           )
         {
             fprintf(stderr, "Fatal error reboot your system\n" );
             abort();