fix: static code analysis, until (dart 3.2.0 fixes)[dart-archive/linter@411a3f5]

Author: RyanCarrier

lib/src/fields/form_builder_date_time_picker.dart

@@ -298,10 +298,11 @@ class _FormBuilderDateTimePickerState extends FormBuilderFieldDecorationState<
         newValue = await _showDatePicker(context, currentValue);
         break;
       case InputType.time:
-        final newTime = await _showTimePicker(context, currentValue);
-        newValue = null != newTime ? convert(newTime) : null;
+        if (!context.mounted) return null;
+        newValue = convert(await _showTimePicker(context, currentValue));
         break;
       case InputType.both:
+        if (!context.mounted) return null;
         final date = await _showDatePicker(context, currentValue);
         if (date != null) {
           if (!mounted) break;