Guard syncTerrain against running before the style has loaded

public/js/overlays.js

@@ -100,6 +100,11 @@ class HillshadeControl {
   // showing raised terrain needs both "tilted enough to see it" and "the
   // DEM source this checkbox controls is actually loaded".
   syncTerrain(pitched) {
+    // setLight/setTerrain throw if the style isn't loaded yet — called
+    // synchronously from map.js's setOverlaysControl during page init,
+    // before the first style.load; that listener re-invokes this once it
+    // actually is loaded, so bailing here just skips the premature call.
+    if (!this._map.isStyleLoaded()) return;
     const terrainOn = pitched && this._active && this._map.getSource(HILLSHADE_ID);
     if (terrainOn) {
       this._map.setTerrain({ source: HILLSHADE_ID, exaggeration: 3 });