Handle cases where module.__file__ is set to None.

I don't know why this would be the case, namespace modules don't have a
__file__ attribute at all when I tried it, but they should just be skipped
anyway.

#4

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=191100585

Author: xinghuadou-google

src/googleclouddebugger/module_utils2.py

@@ -57,7 +57,7 @@ def GetLoadedModuleBySuffix(path):
   """
   root = os.path.splitext(path)[0]
   for module in sys.modules.values():
-    mod_root = os.path.splitext(getattr(module, '__file__', ''))[0]
+    mod_root = os.path.splitext(getattr(module, '__file__', None) or '')[0]
 
     if not mod_root:
       continue