How to reproduce:
1. Acquire a Unity project
2. Execute this in terminal: "./Unity -projectPath /path/to/project -importPackage /random/path/"
(Leave out x.unitypackage file itself from the path. E.g., "./Unity -projectPath ~/project -importPackage ~/")
3. Observe the errors thrown in the Unity Console once Launched:
"Failed to import package with error: Couldn't decompress package"
"Failed importing package"

Expected result: an error is thrown, explaining that a .unitypackage file was not found in the provided file path
Actual result: errors thrown that are confusing for users:
"Failed to import package with error: Couldn't decompress package",
"Failed importing package"

Reproduced with: 5.5.6f1, 5.6.5p2, 2017.1.3p2, 2017.2.2f1, 2017.3.1p3, 2018.1.0b11, 2018.2.0a5