Problem:
The argument to `:help` is normalized to fit the general tag format.
I.e. i^U-default, iCTRL-U-default and i_CTRL_U-default should all point
to the i_CTRL_U-default tag. Our normalization adds an underscore around
the CTRL keycode, e.g. iCTRL-GCTRL-J becomes i_CTRL-G_CTRL-J. That's not
necessary if the following part starts with a dash, like the case of
iCTRL-U-default.
Solution:
Do not insert an underscore if the following character is a dash/minus
(-).
84ae70c172