Fix options page when help-dialog showing.
Fix options page when help-dialog showing.

This allows the user to enter key mappings on the options page with the
help dialog open.

Fixes #2045.

smblott-github/vimium,gdh1995/vimium,willsALMANJ/vimium,poacher2k/vimium,mrmr1993/vimium,gdh1995/vimium,mrmr1993/vimium,gdh1995/vimium,decaffeinate-examples/vimium,poacher2k/vimium,philc/vimium,decaffeinate-examples/vimium,willsALMANJ/vimium,smblott-github/vimium,poacher2k/vimium,philc/vimium,willsALMANJ/vimium,philc/vimium,mrmr1993/vimium,decaffeinate-examples/vimium,smblott-github/vimium