Setting `withPush(true)` does not work as expected on cdk overlay

[alexbjorlig]

Reproduction

Use StackBlitz to reproduce your issue: https://stackblitz.com/fork/components-issue

Steps to reproduce:

1. Open this stackblitz.
2. Follow the steps in this gif (resize window to less than 222px, and open overlay):

Expected Behavior

When viewport height is too low, I expect the overlay to be centered in the viewport. To quote the overlay api withPush:

Sets whether the overlay can be pushed on-screen if none of the provided positions fit.

Actual Behavior

The overlay is positioned with the provided position strategies:

.withPositions([
        {
          panelClass: 'custom-panel1',
          originX: 'center',
          originY: 'center',
          overlayX: 'start',
          overlayY: 'top',
        },
        {
          panelClass: 'custom-panel2',
          originX: 'center',
          originY: 'center',
          overlayX: 'start',
          overlayY: 'bottom',
        },
      ]),

But none of them should be used, because they push the content off-screen.

Environment

• Angular: 8
• CDK/Material: 8
• Browser(s): Version 78.0.3904.87 (Official Build) (64-bit)
• Operating System (e.g. Windows, macOS, Ubuntu): macOS

[PatoDeVille]

any updates on this?