Fix disabled checked switch style

[Smankusors]

Proposed changes

There's a style problem when a switch disabled but checked, the background color should be disabled color, not enabled color.

Reference design

Codepen:

Problem example

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 change).

Checklist:

• I have read the CONTRIBUTING document.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

Note : This is from Dogfalo#6021

[Pierstoval]

Good catch 👍

[DanielRuf]

LGTM

[DanielRuf]

Thanks for your contribution to materializecss.

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