Simplify routine used to get the list of files from git

This change remove duplicated code

src/sugar3/activity/bundlebuilder.py

@@ -169,6 +169,7 @@ class Packager(object):
             os.mkdir(self.config.dist_dir)
 
     def get_files_in_git(self):
+        git_ls = None
         try:
             git_ls = subprocess.Popen(['git', 'ls-files'],
                                       stdout=subprocess.PIPE,
@@ -176,17 +177,14 @@ class Packager(object):
         except OSError:
             logging.warn('Packager: git is not installed, '
                          'fall back to filtered list')
-            return list_files(self.config.source_dir,
-                              IGNORE_DIRS, IGNORE_FILES)
 
+        if git_ls is not None:
             stdout, _ = git_ls.communicate()
             if git_ls.returncode:
                 # Fall back to filtered list
                 logging.warn('Packager: this is not a git repository, '
                              'fall back to filtered list')
-            return list_files(self.config.source_dir,
-                              IGNORE_DIRS, IGNORE_FILES)
-        if stdout:
+            elif stdout:
                 # pylint: disable=E1103
                 git_output = [path.strip() for path in
                               stdout.strip('\n').split('\n')]
@@ -204,7 +202,7 @@ class Packager(object):
                     files = [f for f in files if not fnmatch(f, pattern)]
 
                 return files
-        else:
+
         return list_files(self.config.source_dir,
                           IGNORE_DIRS, IGNORE_FILES)