No tab selected is no longer supported

[larixer]

In tabs demo one can see the text:
If you set the selected tab binding to -1, it will leave no tab selected.

But in reality this is not true. The work around before was to set md-selected="-2" to get no tab selected, but this doesn't work too in latest angular-material, because of:
$scope.selectedIndex = getNearestSafeIndex(newValue);
and getNearestSafeIndex will always select 0 tab if md-selected is negative.

Please support the case when no tab is selected, we need it.