bug(mat-date-range-picker): comparison range not rendered if the range is a single day

[steven509]

Reproduction

StackBlitz: https://stackblitz.com/edit/components-issue-e3gewx

Steps to reproduce:

1. Have a comparison range of a single day
2. Open date range picker

Expected Behavior

What behavior were you expecting to see?
The date range picker to show the single day in the comparison range in yellow

Actual Behavior

What behavior did you actually see?
No comparison range indicated at all in the date range picker

Environment

• Angular: 10.0.3
• CDK/Material: 10.1.0
• Browser(s): All
• Operating System (e.g. Windows, macOS, Ubuntu): All

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