Fixed an error caused by the VASL .vmod not loading properly.

vasl_templates/webapp/vasl_mod.py

@@ -178,6 +178,7 @@ class VaslMod:
         # clean up
         # NOTE: We keep our module and extension ZIP files open for the duration (so we can
         # read images out of them on demand), so we need to make sure we close them here.
+        if hasattr( self, "_files" ):
             for f in self._files:
                 f[0].close()