Fix init of `headerTextStyles`

lib/src/widgets/toolbar/buttons/dropdown_header_style.dart

@@ -37,7 +37,7 @@ class _QuillToolbarSelectHeaderStyleDropdownButtonState
     Attribute.h6: context.loc.heading6,
   };
 
-  late final Map<Attribute, TextStyle> _headerTextStyles;
+  Map<Attribute, TextStyle>? _headerTextStyles;
 
   QuillToolbarSelectHeaderStyleDropdownButtonOptions get options {
     return widget.options;
@@ -100,10 +100,9 @@ class _QuillToolbarSelectHeaderStyleDropdownButtonState
   }
 
   @override
-  void initState() {
-    super.initState();
-    controller.addListener(_didChangeEditingValue);
-    _selectedAttribute = _getHeaderValue();
+  void didChangeDependencies() {
+    super.didChangeDependencies();
+    if (_headerTextStyles == null) {
       final defaultStyles = QuillStyles.getStyles(context, false);
       _headerTextStyles = {
         Attribute.h1: defaultStyles!.h1!.style,
@@ -114,6 +113,14 @@ class _QuillToolbarSelectHeaderStyleDropdownButtonState
         Attribute.h6: defaultStyles.h6!.style,
       };
     }
+  }
+
+  @override
+  void initState() {
+    super.initState();
+    controller.addListener(_didChangeEditingValue);
+    _selectedAttribute = _getHeaderValue();
+  }
 
   @override
   Widget build(BuildContext context) {
@@ -244,7 +251,7 @@ class _QuillToolbarSelectHeaderStyleDropdownButtonState
               header.value,
               style: TextStyle(
                 fontSize: options.renderItemTextStyle
-                    ? _headerTextStyles[header.key]?.fontSize ??
+                    ? _headerTextStyles![header.key]!.fontSize ??
                         DefaultTextStyle.of(context).style.fontSize ??
                         14
                     : null,