ensure linen is defined in find_source_lines

IPython/core/oinspect.py

@@ -326,6 +326,8 b' def find_source_lines(obj):'
             # For instances, try the class object like getsource() does
             if hasattr(obj, '__class__'):
                 lineno = inspect.getsourcelines(obj.__class__)[1]
+            else:
+                lineno = None
     except:
         return None