Handle non-character keys properly in hints mode.
Handle non-character keys properly in hints mode.

Previously, pressing any non-character key would re-show all hints.

Refactored the code in the process to make it more obvious whether we're
handling all possible keypress cases.

dimatter/vimium,Lw-Cui/vimium,jb55/vimium-plus,elderbas/vimium,dimatter/vimium,mrmr1993/vimium,Lw-Cui/vimium,borgified/vimium,tuchangwei/vimium,decaffeinate-examples/vimium,justalittlenoob/vimium,smblott-github/vimium,borgified/vimium,csmalin/vimium,dimatter/vimium,llimllib/vimium,hhsue/vimium,elegantwww/vimium,PrestanceDesign/vimium,tuchangwei/vimium,zhangmin510/vimium,PickRelated/vimium,hhsue/vimium,bkudria/vimium,VPashkov/vimium,elegantwww/vimium,csmalin/vimium,zhangmin510/vimium,smblott-github/vimium,douglas-larocca/vimium,elderbas/vimium,crazypenguincode/vimium,bkudria/vimium,douglas-larocca/vimium,wildeyes/vimium,philc/vimium,Aleroniponi/vimium,decaffeinate-examples/vimium,gdh1995/vimium,douglas-larocca/vimium,smblott-github/vimium-smblott,jb55/vimium-plus,mrmr1993/vimium,justalittlenoob/vimium,poacher2k/vimium,PickRelated/vimium,borgified/vimium,philc/vimium,PrestanceDesign/vimium,justalittlenoob/vimium,Robinson10240/vimium,elegantwww/vimium,mrmr1993/vimium,willsALMANJ/vimium,smblott-github/vimium-smblott,poacher2k/vimium,bkudria/vimium,willsALMANJ/vimium,poacher2k/vimium,VPashkov/vimium,PrestanceDesign/vimium,csmalin/vimium,Lw-Cui/vimium,Aleroniponi/vimium,gdh1995/vimium,smblott-github/vimium,cyrixhero/vimium,gdh1995/vimium,cyrixhero/vimium,PickRelated/vimium,Robinson10240/vimium,zhangmin510/vimium,philc/vimium,VPashkov/vimium,Robinson10240/vimium,wildeyes/vimium,decaffeinate-examples/vimium,cyrixhero/vimium,elderbas/vimium,crazypenguincode/vimium,tuchangwei/vimium,wildeyes/vimium,willsALMANJ/vimium,hhsue/vimium,Aleroniponi/vimium,shaung/vimium