Badge: Fixed default color

[Garderoben]

Description

When no color was set or Default Color was used the badge did not have any background color at all.
Added color to the badge if default color is used.

Before:

After:

How Has This Been Tested?

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• The PR is submitted to the correct branch (dev).
• My code follows the code style of this project.
• I've added relevant tests.

[codecov]

Codecov Report

Merging #3971 (068b2d4) into dev (8f24a0b) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##              dev    #3971   +/-   ##
=======================================
  Coverage   91.12%   91.12%           
=======================================
  Files         351      351           
  Lines       11605    11606    +1     
=======================================
+ Hits        10575    10576    +1     
  Misses       1030     1030           

Impacted Files	Coverage Δ
src/MudBlazor/Components/Badge/MudBadge.razor.cs	89.28% <100.00%> (+0.39%)	⬆️

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