[mkgmap-dev] Commit r4371: Catch invalid value for option mapname (-n) like --mapname=Zambia

Version mkgmap-r4371 was committed by gerd on Fri, 15 Nov 2019 Catch invalid value for option mapname (-n) like --mapname=Zambia Although the option name is mapname we expect the mapid here, an 8-digit number like 63240001 http://www.mkgmap.org.uk/websvn/revision.php?repname=mkgmap&rev=4371