Fix network mock

Signed-off-by: Rahix <rahix@rahix.de>

event.lua

@@ -28,7 +28,7 @@ end
 function event.pullFiltered(timeout, filter)
   while true do
     local msg = table.pack(network.pull())
-    if msg == nil then
+    if msg[1] == nil then
       return nil
     elseif filter(table.unpack(msg)) then
       return table.unpack(msg)

network.lua

@@ -64,18 +64,19 @@ function network.pull()
     local message = inject_message[current_node][1]
     table.remove(inject_message[current_node], 1)
 
-    -- print("pulled "..require("serialization").serialize(message))
-
     -- Actually send the injected message now
+    -- but save the last latest_message
+    local latest = latest_message[current_node]
     table.insert(active_node, message.from)
     network.send(current_node, message.port, message.msg)
     active_node[#active_node] = nil
+    latest_message[current_node] = latest
 
     return "modem_message", current_node, message.from, message.port, 0, message.msg
   end
 
   if latest_message[current_node] == nil then
-    error("Tried to pull while no message was available")
+    return nil
   end
   local message = latest_message[current_node]