Stop if custom IC map does not parse as expected

[caufieldjh]

Right now, if an error is encountered when loading a custom IC map, it raises an error:

Loading custom IC map from: "test_ic.tsv"
Failed to import custom IC map: Line does not contain enough columns

See

semsimian/src/lib.rs

Lines 118 to 129 in e2cba82

	if let Some(custom_ic_map_path) = custom_ic_map_path {
	let path = PathBuf::from(custom_ic_map_path);
	println!("Loading custom IC map from: {:?}", path);
	match import_custom_ic_map(&path) {
	Ok(ic_map) => {
	println!("Custom IC map imported successfully.");
	imported_ic_map.insert(predicate_set_to_key(&Some(predicates.clone())), ic_map);
	}
	Err(e) => eprintln!("Failed to import custom IC map: {}", e),
	}
	}

This should probably end the process before it continues on to build a new IC map, as the user may not notice this error.