[Grid] Potential division by zero with unitStarWidth processing

[jeromelaban]

Current behavior

Potential division by zero in grid layouter: #2128 (comment)

How to reproduce it (as minimally and precisely as possible)

None yet, a repro case is needed.

Environment

Nuget Package: 2.0

Package Version(s):

Affected platform(s):

• iOS
• Android
• WebAssembly
• WebAssembly renderers for Xamarin.Forms
• Windows
• Build tasks
• Solution Templates

Visual Studio:

• 2017 (version: )
• 2019 (version: )
• for Mac (version: )

Relevant plugins:

• Resharper (version: )

Anything else we need to know?