revert list mapping

https://github.com/fleaflet/flutter_map/pull/1594/files/38d7250da5524779449cab91559d1b25234641da..df4b2053e79c71704b02fd72dcfe52bfd28d6888#r1270268326

lib/src/layer/overlay_image_layer.dart

@@ -149,9 +149,10 @@ class OverlayImageLayer extends StatelessWidget {
     final map = MapCamera.of(context);
     return ClipRect(
       child: Stack(
-        children: overlayImages
-            .map((image) => image.buildPositionedForOverlay(map))
-            .toList(growable: false),
+        children: <Widget>[
+          for (var overlayImage in overlayImages)
+            overlayImage.buildPositionedForOverlay(map),
+        ],
       ),
     );
   }