Use both the upper-left corner and the center of a link's bounding box to determine if it's visible.
Use both the upper-left corner and the center of a link's bounding box to determine if it's visible.

I previously switched the logic to use the center of the bounding box, but that does
not work well for multi-line links.

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