Fix inconsistent-return-statements pylint warnings

src/python/grpcio/grpc/_server.py

@@ -329,6 +329,7 @@ class _RequestIterator(object):
             request = self._state.request
             self._state.request = None
             return request
+        raise Exception('gRPC Error: Invalid _state')
 
     def _next(self):
         with self._state.condition:

src/python/grpcio/grpc/_utilities.py

@@ -116,6 +116,8 @@ class _ChannelReadyFuture(grpc.Future):
             callable_util.call_logging_exceptions(
                 done_callback, _DONE_CALLBACK_EXCEPTION_LOG_MESSAGE, self)
 
+        return True
+
     def cancelled(self):
         with self._condition:
             return self._cancelled

src/python/grpcio/grpc/beta/_server_adaptations.py

@@ -305,6 +305,7 @@ def _simple_method_handler(implementation, request_deserializer,
                                         response_serializer, None, None, None,
                                         _adapt_stream_stream_event(
                                             implementation.stream_stream_event))
+    raise ValueError()
 
 
 def _flatten_method_pair_map(method_pair_map):

src/python/grpcio/grpc/beta/utilities.py

@@ -85,6 +85,8 @@ class _ChannelReadyFuture(future.Future):
             callable_util.call_logging_exceptions(
                 done_callback, _DONE_CALLBACK_EXCEPTION_LOG_MESSAGE, self)
 
+        return True
+
     def cancelled(self):
         with self._condition:
             return self._cancelled