Initialize bitmapId field

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@32163 15284696-431f-4ddb-bdfa-cd5b030d7da7

lib/nviz/render.c

@@ -55,6 +55,7 @@ void Nviz_init_render_window(struct render_window *rwin)
 #elif defined(OPENGL_WINDOWS)
     rwin->displayId = NULL;
     rwin->contextId = NULL;
+    rwin->bitmapId = NULL;
 #endif
 }