fix: handle cases where ios build support is not installed

Author: uerceg

Assets/Adjust/Scripts/Editor/AdjustEditor.cs

@@ -9,10 +9,10 @@
 using UnityEditor.Callbacks;
 #if UNITY_IOS
 using UnityEditor.iOS.Xcode;
-#endif
 #if UNITY_2019_3_OR_NEWER
 using UnityEditor.iOS.Xcode.Extensions;
 #endif
+#endif
 
 namespace AdjustSdk
 {