fix(Attribute): prevent null exception from RestrictedAttributeDrawer

The Restricted Attribute Drawer can thrown an exception when using the
Unity Quick Search functionality due to the EditorStyles not being
available to assign to static fields.

Instead these fields are now just assigned in the OnGUI method before
the properties are changed, this seems to resolve the error.

Author: thestonefox

Editor/Data/Attribute/RestrictedAttributeDrawer.cs

@@ -13,23 +13,23 @@ public class RestrictedAttributeDrawer : PropertyDrawer
         /// <summary>
         /// The original GUI enabled state.
         /// </summary>
-        protected static bool originalGUIEnabledState = GUI.enabled;
+        protected static bool originalGUIEnabledState;
         /// <summary>
         /// The original GUI color.
         /// </summary>
-        protected static Color originalGuiColor = GUI.color;
+        protected static Color originalGuiColor;
         /// <summary>
         /// The original font style.
         /// </summary>
-        protected static FontStyle originalFontStyle = EditorStyles.label.fontStyle;
+        protected static FontStyle originalFontStyle;
         /// <summary>
         /// The original normal text color.
         /// </summary>
-        protected static Color originalNormalTextColor = EditorStyles.label.normal.textColor;
+        protected static Color originalNormalTextColor;
         /// <summary>
         /// The original focused text color.
         /// </summary>
-        protected static Color originalFocusedTextColor = EditorStyles.label.focused.textColor;
+        protected static Color originalFocusedTextColor;
         /// <summary>
         /// The color to use for muted text.
         /// </summary>
@@ -42,6 +42,12 @@ public class RestrictedAttributeDrawer : PropertyDrawer
         /// <inheritdoc/>
         public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
         {
+            originalGUIEnabledState = GUI.enabled;
+            originalGuiColor = GUI.color;
+            originalFontStyle = EditorStyles.label.fontStyle;
+            originalNormalTextColor = EditorStyles.label.normal.textColor;
+            originalFocusedTextColor = EditorStyles.label.focused.textColor;
+
             EditorGUI.BeginProperty(position, label, property);
             RestrictedAttribute attrib = (RestrictedAttribute)attribute;
             Behaviour behaviour = (Behaviour)property.serializedObject.targetObject;