stbte: fix layername button growing for both sides

stb_tilemap_editor.h

@@ -3394,7 +3394,7 @@ static void stbte__layers(stbte_tilemap *tm, int x0, int y0, int w, int h)
    int i, y, n;
    int x1 = x0+w;
    int y1 = y0+h;
-   int side = stbte__ui.panel[STBTE__layer].side;
+   int side = stbte__ui.panel[STBTE__panel_layers].side;
    int xoff = tm->has_layer_names ? stbte__region[side].width - 42 : 20;
    xoff = (xoff < tm->layername_width + 10 ? xoff : tm->layername_width + 10);
    static char *propmodes[3] = {