private RowSegment<E> getTopRowSegment() {
		return isFlowingUpwards() ? next : previous;
	}
Returns a bottom y position assuming rows are one million pixels apart for comparison
purposes. It takes into account the assigned offsets of the attached rows. This method
depends on row offsets having already been assigned.
@return a virtual bottom y position only useful for comparison purposes.
Ghidra/Features/FunctionGraph/src/main/java/ghidra/app/plugin/core/functiongraph/graph/layout/flowchart/ColumnSegment.java