FIX: Exceptions when opening new project (case 1313185, #1453).

Author: Rene Damm

Packages/com.unity.inputsystem/CHANGELOG.md

@@ -32,6 +32,7 @@ however, it has to be formatted properly to pass verification tests.
 
 #### Actions
 
+- Fixed opening a new project (or one that needs a full reimport) leading to several exceptions in the console if the most recently opened project was closed with a `.inputactions` editor open ([case 1313185](https://issuetracker.unity3d.com/issues/exceptions-about-previously-open-action-map-being-thrown-when-opening-new-project)).
 - Fixed incorrect indentation of input actions in the inspector ([case 1285546](https://issuetracker.unity3d.com/product/unity/issues/guid/1285546/)).
 - Fixed an issue where serialized `InputAction` properties would have display name "Input Action" in the Inspector window instead of their given name. ([case 1367240](https://issuetracker.unity3d.com/product/unity/issues/guid/1367240)).
 - Fixed an issue where `InputAction.Enable` would not reuse memory allocated prior and thus lead to memory leaks ([case 1367442](https://issuetracker.unity3d.com/issues/input-system-puts-a-lot-of-pressure-on-the-garbage-collector-when-enabling-and-disabling-inputactionmaps)).

Packages/com.unity.inputsystem/InputSystem/Editor/AssetEditor/InputActionAssetManager.cs

@@ -29,10 +29,7 @@ public string path
             get
             {
                 Debug.Assert(!string.IsNullOrEmpty(m_AssetGUID), "Asset GUID is empty");
-                var assetPath = AssetDatabase.GUIDToAssetPath(m_AssetGUID);
-                if (string.IsNullOrEmpty(assetPath))
-                    throw new InvalidOperationException("Could not determine asset path for " + m_AssetGUID);
-                return assetPath;
+                return AssetDatabase.GUIDToAssetPath(m_AssetGUID);
             }
         }
 
@@ -133,7 +130,17 @@ public void Cleanup()
 
         public void LoadImportedObjectFromGuid()
         {
-            m_ImportedAssetObject = AssetDatabase.LoadAssetAtPath<InputActionAsset>(path);
+            // https://fogbugz.unity3d.com/f/cases/1313185/
+            // InputActionEditorWindow being an EditorWindow, it will be saved as part of the editor's
+            // window layout. When a project is opened that has no Library/ folder, the layout from the
+            // most recently opened project is used. Which means that when opening an .inputactions
+            // asset in project A, then closing it, and then opening project B, restoring the window layout
+            // also tries to restore the InputActionEditorWindow having that very same asset open -- which
+            // will lead nowhere except there happens to be an InputActionAsset with the very same GUID in
+            // the project.
+            var assetPath = path;
+            if (!string.IsNullOrEmpty(assetPath))
+                m_ImportedAssetObject = AssetDatabase.LoadAssetAtPath<InputActionAsset>(assetPath);
         }
 
         public void ApplyChanges()