_lp_svn_branch: fix usage of maybe undef variable 'root'
_lp_svn_branch: fix usage of maybe undef variable 'root'

smadhueagle/liquidprompt,tsbarnes/liquidprompt,pkkolos/liquidprompt,dpilone/liquidprompt,jaesivsm/liquidprompt,dtschan/liquidprompt,joshuarubin/dotfiles,joshuarubin/dotfiles,milouse/liquidprompt,dan-cleinmark/liquidprompt,alexprengere/liquidprompt,joshuarubin/dotfiles,BobHood/liquidprompt,joshuarubin/dotfiles,laurentbardin/liquidprompt,nojhan/liquidprompt