Ignore IOError when checking Python file

Emacs uses a symbolic link to non-existing file for locking file.
It has the same extension as the original file.  Therefore, Jedi
must ignore IOError when trying to open this symbolic file.

jedi/dynamic.py

@@ -33,7 +33,10 @@ def check_python_file(path):
         try:
             return builtin.CachedModule.cache[path][1].module
         except KeyError:
-            return check_fs(path)
+            try:
+                return check_fs(path)
+            except IOError:
+                return None
 
     def check_fs(path):
         with open(path) as f: