Handle invalid values in ResizeableItemFrameViewModel

If the maxSpans is less than the currentSpans, the anchors are
calculated incorrectly which leads to a crash in SystemUI. This fix
ensures that we always coerce the max to be at least the current spans.

This can happen when Compose is initializing, and the padding values
haven't been finalized yet. In this intermediate state, we may receive
invalid values before the grid stabilizes.

Fixes: 376490959
Test: atest ResizeableItemFrameViewModelTest
Flag: com.android.systemui.communal_widget_resizing
Change-Id: Ic9b569fb1894b950882aeaeea5065c99c762dc74