This function is used in the Team Arena menus
I don't think it's actually possible to reach this line with
foundPlayerServerNames < 1, because by the time we get here we have
set it to 1 + the actual number of servers; but if we did, it would
clearly underflow into foundPlayerServerNames[-1], which would be
undefined behaviour. gcc 6 diagnoses this with a warning:
code/ui/ui_main.c: In function ‘UI_BuildFindPlayerList’:
code/ui/ui_main.c:4138:16: warning: array subscript is below array bounds [-Warray-bounds]
Also correct the sizeof() invocation to make it more obviously
correct (in fact the buffers for names and addresses happen to both
be of size MAX_ADDRESSLENGTH, so it was fine, but it's good to be
obvious).