fix: coerce nullable autofocus for Material button icons (Flutter 3.41+)

Author: wlangdon2-cmd

lib/src/platform/platform_filled_button_icon.dart

@@ -44,7 +44,7 @@ class PlatformFilledButtonIcon extends StatelessWidget {
         style: style,
         focusNode: focusNode,
         clipBehavior: clipBehavior,
-        autofocus: autofocus,
+        autofocus: autofocus ?? false,
       ),
       cupertino: (context, platform) => CupertinoButton.filled(
         padding: EdgeInsets.all(8.0),

lib/src/platform/platform_text_button_icon.dart

@@ -44,7 +44,7 @@ class PlatformTextButtonIcon extends StatelessWidget {
         style: style,
         focusNode: focusNode,
         clipBehavior: clipBehavior,
-        autofocus: autofocus,
+        autofocus: autofocus ?? false,
       ),
       cupertino: (context, platform) => CupertinoButton(
         color: backgroundColor,