Add a special handling for fs_manifest key-value pair

[ostrosablin]

Some servers return fs_manifest key-value pair, which has it's value
split by newline, followed by a space. qstat breaks on such servers (at
least, it can't fetch the rules and players, because it treats newline
as beginning of player data, an unexpected data causes qstat to break
with error).

One such example is server run by my colleague, at 52.59.239.15:57131

Raw data from socket:

b'\xff\xff\xff\xffstatusResponse\n\\fs_cdn\\84.252.132.60:9000\\dmflags\\0\\fraglimit\\25\\timelimit\\15\\g_gametype\\4\\sv_privateClients\\0\\sv_hostname\\The Quake CTF (VQ3)\\sv_maxclients\\24\\sv_minRate\\0\\sv_maxRate\\30000\\sv_dlRate\\2000\\sv_minPing\\0\\sv_maxPing\\0\\sv_floodProtect\\0\\sv_allowDownload\\1\\sv_dlURL\\http://84.252.132.60:8000\\g_maxGameClients\\0\\sv_fps\\30\\server_gameplay\\VQ3\\version\\ioq3 1.36 linux-x86_64 Apr 23 2021\\com_gamename\\Quake3Arena\\com_protocol\\71\\mapname\\q3wcp18\\fs_manifest\\baseq3/pak100.pk3@2388798635@16506992\n baseq3/pak101.pk3@2206768903@2657563\n baseq3/pak102.pk3@2076841188@3024290\n baseq3/q3wcp18.pk3@2233822267@7704683\n cpma/z-cpma-pak152.pk3@3054920672@8135165\n linuxq3ademo-1.11-6.x86.gz.sh@857908472@49289300\n linuxq3apoint-1.32b-3.x86.run@296843703@30923961\n \\game\\CPMA\\gamename\\cpma\\gamedate\\Apr 03 2019\\gameversion\\1.52\\sv_arenas\\1\\Score_Time\\Warmup\\Score_Red\\0\\Score_Blue\\0\\Players_Blue\\1 \\GTV_CN\\1\\g_needpass\\0\\mode_current\\PUBCTF\n0 34 "UltraBloxX"\n'

Example of qstat run:

qstat -P -q3s 52.59.239.15:57131
ADDRESS           PLAYERS      MAP   RESPONSE TIME    NAME
52.59.239.15:57131    ERROR < baseq3/pak101.pk3@2206768903@2657563>

Following patch implements special handling for fs_manifest key, that ignores newline as a separator, while keeping all other parsing intact, so it fixes qstat to handle this server correctly, while it shouldn't break anything else.

[ostrosablin]

This key-value pair (fs_manifest) seems to be related to QuakeJS (Emscripten support related). If I understand correctly, it contains list of maps and resources that QuakeJS web clients need to download to be able to join game. That's why it's subvalues are separated by newline + space.

It's defined here in upstream ioquake code

https://github.com/ioquake/ioq3/blob/4f7d7bf2159aa0a18b79bb417aa760abac817b2a/code/qcommon/files.c#L261

[ostrosablin]

I've also corrected display_json.c (function json_escape) to properly escape newlines because otherwise JSON would be invalid and useless for further processing.