protected boolean checkIsValid() {
		return checkIsValid(null);
	}
Check whether this object is still valid. If the object is invalid, the object will attempt
to refresh itself. If the refresh fails, the object will be marked as deleted.

@return true if the object is valid, else false if deleted
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/database/DatabaseObject.java