[algorithm] Improve algorithm process signature check

Now both invalid case are treated as exception:
- Calling a loop using algorithm without loop_channel
- Calling a non loop using alggorithm with a loop_channel

beat/backend/python/algorithm.py

@@ -257,13 +257,16 @@ class Runner(object):
             elif self.algorithm.type == Algorithm.AUTONOMOUS:
                 run_args = [self.obj, 'process', self.exc, data_loaders, outputs_to_use]
 
-                if loop_channel:
-                    sig = signature(self.obj.process)
-                    params = sig.parameters
+                sig = signature(self.obj.process)
+                params = sig.parameters
+
+                if loop_channel is not None:
                     if 'loop_channel' in params:
                         run_args.append(loop_channel)
                     else:
                         raise exc("Algorithm '%s' is not a valid loop enabled algorithm" % self.name)
+                elif 'loop_channel' in params:
+                    raise exc("Algorithm '%s' is a loop enabled algorithm but no loop_channel given" % self.name)
 
                 return loader.run(*run_args)
 
@@ -287,7 +290,6 @@ class Runner(object):
         if not self.prepared:
             raise exc("Algorithm '%s' is not yet prepared" % self.name)
 
-
         answer = loader.run(self.obj, 'validate', self.exc, result)
 
         if not isinstance(answer, tuple):