misc/mc: Fix SUBSHELL blank terminal upon opening in xterm with Slang

Note: Unfortunately this does not fix this issue on the FreeBSD console.

PR: 217758
Submitted by: Alexander Moisseev <moiseev@mezonplus.ru>
Reported by: Dron <dron_2@ua.fm>
Reported by: danfe
MFH: 2017Q4