Partially fix #4098.

This is, however, only a half fix as this fixes that it fails when
there's None in waiting_descriptors[2], but actually, there never
should be None, so I have to investigate why there was none.

This patch is, however, correct and needed and the other queues also
have that check. It's just that I also need to fix the reason for
the None in the queue.

src/common/xmpp/idlequeue.py

@@ -204,16 +204,18 @@ class SelectIdleQueue(IdleQueue):
 		except select.error, e:
 			waiting_descriptors = ((),(),())
 			if e[0] != 4: # interrupt
-				raise
-		for fd in waiting_descriptors[0]:
-			q = self.queue.get(fd)
-			if q:
+				raise
+		for fd in waiting_descriptors[0]:
+			q = self.queue.get(fd)
+			if q:
 				q.pollin()
 		for fd in waiting_descriptors[1]:
-			q = self.queue.get(fd)
-			if q:
+			q = self.queue.get(fd)
+			if q:
 				q.pollout()
 		for fd in waiting_descriptors[2]:
-			self.queue.get(fd).pollend()
+			q = self.queue.get(fd)
+			if q:
+				q.pollend()
 		self.check_time_events()
 		return True