[ fix #891 ] Cast branch output if HEAD not exists

Author: equt

bin/git-browse

@@ -2,7 +2,7 @@
 
 if [[ $1 == "" ]]
 then
-    branch=$(git rev-parse --abbrev-ref HEAD)
+    branch=$(git rev-parse --abbrev-ref HEAD 2&> /dev/null)
     remote=$(git config branch."${branch}".remote || echo "origin")
 else
     remote=$1