msgpack-gen: Fix for Lua 5.1. (#4857)

goto statement was only introduced in Lua 5.2.

scripts/msgpack-gen.lua

@@ -64,9 +64,7 @@ for i = 1, #arg - 1 do
   local tmp = grammar:match(input:read('*all'))
   for i = 1, #tmp do
     local fn = tmp[i]
-    if fn.noexport then
-      goto continue
-    end
+    if not fn.noexport then
       functions[#functions + 1] = tmp[i]
       if #fn.parameters ~= 0 and fn.parameters[1][2] == 'channel_id' then
         -- this function should receive the channel id
@@ -81,7 +79,7 @@ for i = 1, #arg - 1 do
         -- for specifying errors
         fn.parameters[#fn.parameters] = nil
       end
-    ::continue::
+    end
   end
   input:close()
 end