Steps to reproduce:
1. Create and open a new project with the "Input System" package
2. Create a new folder in the Project window and open it
3. In the toolbar press "Assets" > "Create" > "Input Actions"
4. Select the Input Action asset you have created and press "Edit Asset" in the Inspector window
5. In the Input Action editing window create a new Action Map
6. In the Project window rename the folder containing the Input Action asset
7. In the Input Action editing window press "Save Asset"

Expected result: No errors appear in the Console window, Input Action asset gets saved
Actual result: An error appears in the Console window: "DirectoryNotFoundException: Could not find a part of the path", the Input Action asset does not get saved

Reproducible with: 2018.4.15f1, 2019.2.18f1, 2019.3.0f4, 2020.1.0a19 ("Input System" package version 0.2.1.preview - 1.0.0)
Could not test with: 2017.4 (No package manager)