Allow git packages to be built using local cache if no network is available

satellites/functions/vcs/git.sh

@@ -11,8 +11,9 @@ vcs_git() {
     else
         cd "$dir"
 
-        git fetch > /dev/null
+        if git fetch > /dev/null; then
             git reset --hard FETCH_HEAD > /dev/null
+        fi
         local rev="$(git rev-parse @)"
         if [ "$rev" != "$(cat "${dir}_rev_$_satname" 2> /dev/null || true)" ]; then
             echo "$rev" > "${dir}_rev_$_satname"