inspect.signature throws weird errors sometimes, just make it a bit simpler

Fixes #1031

jedi/evaluate/compiled/access.py

@@ -399,7 +399,13 @@ class DirectObjectAccess(object):
                          or obj.__new__ != object.__new__)):
                 raise ValueError
 
-        signature = inspect.signature(obj)
+        try:
+            signature = inspect.signature(obj)
+        except (RuntimeError, TypeError):
+            # Reading the code of the function in Python 3.6 implies there are
+            # at least these errors that might occur if something is wrong with
+            # the signature. In that case we just want a simple escape for now.
+            raise ValueError
         return [
             SignatureParam(
                 name=p.name,

test/test_api/test_classes.py

@@ -164,6 +164,15 @@ def test_completion_params(Script):
     assert [p.name for p in c.params] == ['s', 'sep']
 
 
+def test_hashlib_params(Script, environment):
+    if environment.version_info < (3,):
+        pytest.skip()
+
+    script = Script(source='from hashlib import ', line=1, column=20)
+    c = script.completions()
+    assert c[2].params
+
+
 def test_signature_params(Script):
     def check(defs):
         params = defs[0].params