check-code: fix check for trailing whitespace on empty lines
It seems like the intention with c7d23b4ca4ba was to catch lines with only
one whitespace too.
hg debuginstall
$ hg debuginstall
checking encoding (ascii)...
checking installed modules (*mercurial)... (glob)
checking templates (*mercurial?templates)... (glob)
checking commit editor...
checking username...
no problems detected
hg debuginstall with no username
$ HGUSER= hg debuginstall
checking encoding (ascii)...
checking installed modules (*mercurial)... (glob)
checking templates (*mercurial?templates)... (glob)
checking commit editor...
checking username...
no username supplied (see "hg help config")
(specify a username in your configuration file)
1 problems detected, please check your install!
[1]