fix GetTexture2D (field picture)

Assets/SibylSystem/MonoHelpers/UIHelper.cs

@@ -734,7 +734,11 @@ public static class UIHelper
     }
 
     public static Texture2D GetTexture2D(string path)
-    {
+    {
+        if (!File.Exists(path))
+        {
+            return null;
+        }
         var pic = new Texture2D(0, 0);
         pic.LoadImage(File.ReadAllBytes(path));
         return pic;