Issue 3967 - Properly handle non-existing file-mappings

packager.py

 # This Source Code Form is subject to the terms of the Mozilla Public
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 # Note: These are the base functions common to all packagers, the actual
 # packagers are implemented in packagerGecko and packagerChrome.
 
 import sys
 import os
 import re
@@ skipping 83 matching lines @@
         return relpath.split('/')[0] in self.includedFiles
 
     def is_ignored(self, relpath):
         parts = relpath.split('/')
         return any(part in self.ignoredFiles for part in parts)
 
     def read(self, path, relpath='', skip=()):
         if os.path.isdir(path):
             for file in os.listdir(path):
                 name = relpath + ('/' if relpath != '' else '') + file
-                if (name not in skip
-                        and self.isIncluded(name) and not self.is_ignored(name)):
+
+                included = self.isIncluded(name) and not self.is_ignored(name)
+                if name not in skip and included:
                     self.read(os.path.join(path, file), name, skip)
         else:
             with open(path, 'rb') as file:
                 if relpath in self:
                     print >>sys.stderr, 'Warning: File %s defined multiple times' % relpath
                 self[relpath] = file.read()
 
     def readMappedFiles(self, mappings):
         for item in mappings:
             target, source = item
@@ skipping 19 matching lines @@
 
     def zip(self, outFile, sortKey=None, compression=zipfile.ZIP_DEFLATED):
         with zipfile.ZipFile(outFile, 'w', compression) as zf:
             for name in sorted(self, key=sortKey):
                 zf.writestr(name, self[name])
 
     def zipToString(self, sortKey=None):
         buffer = StringIO()
         self.zip(buffer, sortKey=sortKey)
         return buffer.getvalue()