autogen.sh: Correctly detect .git as a file

One of my previous patches 5cfe0d3 tried to handle the case when
libvirt is a submodule of another project. In that case, the .git is
just a link to the parent .git directory (which the autogen.sh script
didn't count on). The fix was missing 'test' though.

autogen.sh

@@ -64,7 +64,7 @@ bootstrap_hash()
 # like to run 'git clean -x -f po' to fix it; but only ./bootstrap regenerates
 # the required file po/Makevars.
 # Only run bootstrap from a git checkout, never from a tarball.
-if test -d .git || -f .git; then
+if test -d .git || test -f .git; then
     curr_status=.git-module-status t=
     if test "$no_git"; then
         t=no-git