Based on a bug report from beta testers in 2010. mintrap()
already had partial checks for this (now fire vortex also burns
a web, as per suggestion in the bug report) but mfndpos()
lacked checks so mintrap() code was almost never exercised.
read_config_file() has used a buffer of size (4 * BUFSZ) since 3.4.x
so parse_config_line() needs a buffer of the same size to avoid
buffer overrun. Allows my old .nethackrc to work again.
David Cohrs