make sure we always have an extension

apps/files/models.py

@@ -103,7 +103,7 @@ class File(amo.models.OnChangeMixin, amo.models.ModelBase):
     def from_upload(cls, upload, version, platform, parse_data={}):
         f = cls(version=version, platform=platform)
         upload.path = path.path(nfd_str(upload.path))
-        f.filename = f.generate_filename(extension=upload.path.ext)
+        f.filename = f.generate_filename(extension=upload.path.ext or '.xpi')
         f.size = int(max(1, round(upload.path.size / 1024, 0)))  # Kilobytes.
         f.jetpack_version = cls.get_jetpack_version(upload.path)
         f.hash = upload.hash

apps/files/tests/test_models.py

@@ -466,6 +466,13 @@ class TestFileFromUpload(UploadTest):
         f = File.from_upload(upload, self.version, self.platform)
         eq_(f.filename, 'xxx-0.1-mac.xpi')
 
+    def test_filename_no_extension(self):
+        upload = self.upload('jetpack')
+        # Remove the exension.
+        upload.name = upload.name.rsplit('.', 1)[0]
+        f = File.from_upload(upload, self.version, self.platform)
+        eq_(f.filename, 'xxx-0.1-mac.xpi')
+
     def test_file_validation(self):
         upload = self.upload('jetpack')
         file = File.from_upload(upload, self.version, self.platform)