Only delete corrupt pickle config files if they exist

os.remove() raises OSError if the file being removed doesn't exist.
Check before calling to ensure we don't raise a useless exception
on an already deleted file.

Change-Id: I44c1c7dd97a47fcab8afb6c18fdf179158b6dab7
Signed-off-by: Shawn O. Pearce <sop@google.com>

git_config.py

@@ -257,9 +257,11 @@ class GitConfig(object):
       finally:
         fd.close()
     except IOError:
-      os.remove(self._pickle)
+      if os.path.exists(self._pickle):
+        os.remove(self._pickle)
     except cPickle.PickleError:
-      os.remove(self._pickle)
+      if os.path.exists(self._pickle):
+        os.remove(self._pickle)
 
   def _ReadGit(self):
     """