bug(null-safety): LateInitializationError: Local firstIndex has not been initialized.

[cpboyd]

If neither the if nor else if triggers to initialize the firstIndex, then this code will fail as it remains uninitialized:

flutter_staggered_grid_view/lib/src/widgets/sliver.dart

Lines 124 to 133 in 3b835ed

	late final int firstIndex;
	late final int lastIndex;
	if (_childElements.isEmpty) {
	firstIndex = 0;
	lastIndex = 0;
	} else if (_didUnderflow) {
	firstIndex = _childElements.firstKey()!;
	lastIndex = _childElements.lastKey()! + 1;
	}
	for (int index = firstIndex; index <= lastIndex; ++index) {

[cpboyd]

The fix was merged