. Remove an assert() which asserts that if isatty() is true then
ttyname() must not return NULL. This isn't entirely true according
to the manual page (the device must be able to be found as well) and
certainly appears to not necessarily be true in the package building
environment on bento (plus at least the PR submitter's environment).
Note that this assert() was, of course, only ever triggered when
running in debug mode (which most people don't, but does happen
during the build in some parts). Also note that there is a check
for isatty() preceding the call for ttyname() and a NULL return
from ttyname() is handled, so removing this assert should not
create any problems.