Method pullBack

The pull-back is performed through a given p-code \b op and set \b this to the resulting range (if possible). If there is a single unknown input, and the set of values for this input that cause the output of \b op to fall into \b this form a range, then set \b this to the range (the "pullBack") and return the unknown varnode. Return null otherwise. We may know something about the input varnode in