go.tools/cmd/cover: don't assume code is gofmt'd
go.tools/cmd/cover: don't assume code is gofmt'd

We want to make an if look like two blocks and have the coverage
report for the else block decorate the "else" keyword with the right
color. To do this, we adjust the apparent starting point of the else
block to include the "else".

The previous code assumed the way to do this was to move the
width of "else " backwards from the else block's opening brace, but
that assumes there is a space there. Instead, we now just start the
else block exactly at the end of the if block. Simpler, cleaner, and
fixes a bug.

Fixes golang/go#8557.

LGTM=gri
R=gri
CC=golang-codereviews
https://golang.org/cl/127620043

cw2018/tools,magiccao/tools,nicot/tools,dmitris/tools,syreclabs/go-tools,argandas/tools,dmitris/tools,golang/tools,syreclabs/go-tools,cw2018/tools,cw2018/tools,dmitris/tools,jdhenke/tools,jdhenke/tools,sshetty10/tools,4ad/tools,runcom/tools,springning/tools,argandas/tools,golang/tools,cmars/tools,matryer/tools,dmitris/tools,syreclabs/go-tools,sshetty10/tools,4ad/tools,jdhenke/tools,cw2018/tools,cmars/tools,runcom/tools,magiccao/tools,argandas/tools,nicot/tools,josharian/tools,glasser/golang-tools,syreclabs/go-tools,matryer/tools,matryer/tools,springning/tools,runcom/tools,josharian/tools,glasser/golang-tools,golang/tools,maddyonline/tools,springning/tools,nicot/tools,magiccao/tools,jdhenke/tools,glasser/golang-tools,golang/tools,maddyonline/tools,glasser/golang-tools,4ad/tools,josharian/tools,runcom/tools,maddyonline/tools,syreclabs/go-tools,syreclabs/go-tools,josharian/tools,cmars/tools,cmars/tools,nicot/tools,matryer/tools,golang/tools,sshetty10/tools,magiccao/tools,springning/tools,sshetty10/tools,argandas/tools,maddyonline/tools