minor optimization from Will Bond in openresty#10.

Author: agentzh

lib/resty/upload.lua

@@ -97,12 +97,12 @@ end
 local function discard_line(self)
  local read_line = self.read_line
 
- local line, err = self.read_line(MAX_LINE_SIZE)
+ local line, err = read_line(MAX_LINE_SIZE)
  if not line then
  return nil, err
  end
 
- local dummy, err = self.read_line(1)
+ local dummy, err = read_line(1)
  if dummy then
  return nil, "line too long: " .. line .. dummy .. "..."
  end