pylightning: Always assign the `init` method in plugin

Also fixes a crash if the doc was empty.

contrib/pylightning/lightning/plugin.py

@@ -295,12 +295,12 @@ class Plugin(object):
                 continue
 
             doc = inspect.getdoc(func)
-            doc = re.sub('\n+', ' ', doc)
             if not doc:
                 self.log(
                     'RPC method \'{}\' does not have a docstring.'.format(name)
                 )
                 doc = "Undocumented RPC method from a plugin."
+            doc = re.sub('\n+', ' ', doc)
 
             methods.append({
                 'name': name,