Specify that buffer size for tox_conference_peer_get_name is given by $size

[zugz]

This change is 

[codecov]

Codecov Report

Merging #1302 into master will decrease coverage by 0.4%.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           master   #1302     +/-   ##
========================================
- Coverage    83.4%   82.9%   -0.5%     
========================================
  Files          82      82             
  Lines       14978   14978             
========================================
- Hits        12495   12423     -72     
- Misses       2483    2555     +72

Impacted Files	Coverage Δ
toxcore/crypto_core_test.cc	90.3% <0%> (-9.7%)	⬇️
toxcore/TCP_client.c	64.6% <0%> (-2.9%)	⬇️
toxcore/LAN_discovery.c	83% <0%> (-2.9%)	⬇️
toxcore/TCP_server.c	80.3% <0%> (-2.6%)	⬇️
toxav/msi.c	64.2% <0%> (-2.6%)	⬇️
toxcore/net_crypto.c	93.6% <0%> (-1.8%)	⬇️
toxav/toxav.c	67.9% <0%> (-1.7%)	⬇️
toxcore/friend_connection.c	94.9% <0%> (-1.2%)	⬇️
toxcore/Messenger.c	86.8% <0%> (-0.2%)	⬇️
toxcore/onion_client.c	96% <0%> (ø)	⬆️

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