[unity] Fixed UPM package Index out of bounds exception in editor code. Closes #2095.

spine-unity/Assets/Spine/Editor/spine-unity/Editor/Utility/SpineEditorUtilities.cs

@@ -172,11 +172,12 @@ namespace Spine.Unity.Editor {
 
 			if (EditorApplication.isPlayingOrWillChangePlaymode) return;
 
-			string[] assets = AssetDatabase.FindAssets("t:script SpineEditorUtilities");
+			string[] folders = { "Assets", "Packages" };
+			string[] assets = AssetDatabase.FindAssets("t:script SpineEditorUtilities", folders);
 			string assetPath = AssetDatabase.GUIDToAssetPath(assets[0]);
 			editorPath = Path.GetDirectoryName(assetPath).Replace('\\', '/');
 
-			assets = AssetDatabase.FindAssets("t:texture icon-subMeshRenderer");
+			assets = AssetDatabase.FindAssets("t:texture icon-subMeshRenderer", folders);
 			if (assets.Length > 0) {
 				assetPath = AssetDatabase.GUIDToAssetPath(assets[0]);
 				editorGUIPath = Path.GetDirectoryName(assetPath).Replace('\\', '/');