Remove unused functions from null_main.c and null_input.c

Sys_mkdir is suppose to have a capital M, which is also in null_main.c.
Fix incorrect strncat usage in CL_ServerInfoPacket
Fix incorrect rgbGen const reading uninitialized memory

If ParseVector fails, color isn't fully set.
Remove a numIboIndexes=0 that is not read from GL2 tr_bsp.c

numIboIndexes is set to 0 inside the loop for each surface. Does not need to be set before loop.