cleanup: Changes for c++17

[stickz]

This cleanup adjusts the rTorrent code to comply with c++17 standard. It also simplifies various parts of the code.

[rakshasa]

(lldb) target create "/prefix/bin/rtorrent"
Current executable set to '/prefix/bin/rtorrent' (x86_64).
(lldb) settings set -- target.run-args  "-o" "system.daemon.set=true,import=/run/self/rc"
(lldb) settings set target.disable-aslr false
(lldb) run
rtorrent: Junk at end of input.
Process 106 exited with status = 255 (0x000000ff)

Getting this error.

[stickz]

(lldb) target create "/prefix/bin/rtorrent"
Current executable set to '/prefix/bin/rtorrent' (x86_64).
(lldb) settings set -- target.run-args  "-o" "system.daemon.set=true,import=/run/self/rc"
(lldb) settings set target.disable-aslr false
(lldb) run
rtorrent: Junk at end of input.
Process 106 exited with status = 255 (0x000000ff)

Getting this error.

All fixed.

  if (first != last) {
    if (!command_map_is_newline(*first))
      throw torrent::input_error("Junk at end of input.");


    first++;
  }

[rakshasa]

It needs to check all from first to last.

[stickz]

It needs to check all from first to last.

This does the same thing as before the cleanup in src/rpc/parse_commands.cc. If we want to change the behavior of
parse_command(target_type target, const char* first, const char* last), I think we should create a new pull request. This pull request just cleans up the code to comply with the c++17 standard. It doesn't change the algorithm of the function.