fix(radio): deselect button if value doesn't match up with the group anymore

[crisbeto]

Handles the case where a radio button is selected and then its value is changed to something that doesn't match up with the group anymore.

[devversion]

LGTM

[jelbourn]

LGTM

[andrewseguin]

This change depends on the order Angular sets the button's checked and value properties. When checked is set before value, both the group and button will have a null value and never be selected. However, when value is set first, the evaluation shows that group's value is null and the button has a value so it sets it.

You can test it by comparing the group value between these two cases:

<!-- No button will be selected since the checked setter was called first and it found that the group and buttons all have null values -->
<mat-radio-group>
  <mat-radio-button checked value="1"> Option 1 </mat-radio-button>
  <mat-radio-button value="2"> Option 2 </mat-radio-button>
  <mat-radio-button value="3"> Option 3 </mat-radio-button>
</mat-radio-group>

<!-- The first button will be selected because checked will update the group based on the first button's value -->
<mat-radio-group>
  <mat-radio-button value="1" checked> Option 1 </mat-radio-button>
  <mat-radio-button value="2"> Option 2 </mat-radio-button>
  <mat-radio-button value="3"> Option 3 </mat-radio-button>
</mat-radio-group>