Allows only one level of recursion

Summary:
When one enters the underscore in the vim bar,
it infinitely recurses trying to process the
key pressed event [1].

This patch allows only one level of recursion.

[1] https://bugs.kde.org/show_bug.cgi?id=364650

Reviewers: cullmann, #kate, sstjames

Subscribers: kwrite-devel

Differential Revision: https://phabricator.kde.org/D2597