public PcodeBlock findLevelBlock(int ind) {
		return findBlock(sortlist, ind);
	}
Assume blocks are in index order, find the block with index -ind-
@param ind is the block index to match
@return the matching PcodeBlock
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/model/pcode/BlockMap.java