fix compile error from AssetSettingsProvider

Author: vkovec

com.unity.formats.fbx/Editor/FbxExportSettings.cs

@@ -242,6 +242,7 @@ static SettingsProvider CreateFbxExportSettingsProvider()
 
             var provider = AssetSettingsProvider.CreateProviderFromObject(
                 "Project/Fbx Export", ExportSettings.instance, GetSearchKeywordsFromGUIContentProperties(typeof(Style)));
+#if UNITY_2019_1_OR_NEWER
             provider.inspectorUpdateHandler += () =>
             {
                 if (provider.settingsEditor != null &&
@@ -250,6 +251,16 @@ static SettingsProvider CreateFbxExportSettingsProvider()
                     provider.Repaint();
                 }
             };
+#else
+            provider.activateHandler += (searchContext, rootElement) =>
+            {
+                if (provider.settingsEditor != null &&
+                    provider.settingsEditor.serializedObject.UpdateIfRequiredOrScript())
+                {
+                    provider.Repaint();
+                }
+            };
+#endif // UNITY_2019_1_OR_NEWER
             return provider;
         }