imp: only return stack if overlay is given

@@ -255,11 +255,23 @@ class _MobileScannerState extends State<MobileScanner>
 
           _controller.updateScanWindow(scanWindow);
         }
-
+        if (widget.overlay != null) {
           return Stack(
             alignment: Alignment.center,
             children: [
-                ClipRect(
+              _scanner(value.size, value.webId, value.textureId),
+              widget.overlay!
+            ],
+          );
+        } else {
+          return _scanner(value.size, value.webId, value.textureId);
+        }
+      },
+    );
+  }
+
+  Widget _scanner(Size size, String? webId, int? textureId) {
+    return ClipRect(
       child: LayoutBuilder(
         builder: (_, constraints) {
           return SizedBox.fromSize(
@@ -267,22 +279,16 @@ class _MobileScannerState extends State<MobileScanner>
             child: FittedBox(
               fit: widget.fit,
               child: SizedBox(
-                            width: value.size.width,
-                            height: value.size.height,
+                width: size.width,
+                height: size.height,
                 child: kIsWeb
-                              ? HtmlElementView(viewType: value.webId!)
-                              : Texture(textureId: value.textureId!),
+                    ? HtmlElementView(viewType: webId!)
+                    : Texture(textureId: textureId!),
               ),
             ),
           );
         },
       ),
-                ),
-                if (widget.overlay != null)
-                  widget.overlay!
-              ],
-            );
-      },
     );
   }