only do git stash save/pop if we have a non-empty working tree (openS…

…USE#228)

Thanks to openSUSE#209 sometimes our working tree will be empty.  In
that case don't try to stash a bunch of changes which effectively
delete the whole working tree and then re-pop them after switching
version.

Fixes openSUSE#228.

TarSCM/scm/git.py

@@ -3,6 +3,8 @@
 import re
 import sys
 
+from glob import glob
+
 from TarSCM.scm.base import Scm
 
 
@@ -44,7 +46,8 @@ def switch_revision(self):
         for rev in revs:
             if self._ref_exists(rev):
                 found_revision = True
-                if os.getenv('OSC_VERSION'):
+                if os.getenv('OSC_VERSION') and \
+                   len(glob(self.clone_dir + "/*")) > 0:
                     stash_text = self.helpers.safe_run(
                         self._get_scm_cmd() +
                         ['stash'],