The '-l' (loop) option would cause the JS runtime to be destroyed and
recreated for each new execution of the script, which resulted in memory
leaks in Windows builds (see issue #672 for details). So instead, just
use a single JS runtime here when the -l option is used to prevent that
from happening, though truth be told, that's likely not a normal/common
occurrence. Other apparent JS-related memory leaks (e.g. in the web
server) appear to be of a common concern.

Likely upgrading to a modern libmozjs would also fix this issue, but
we're far short of being able to do that right now.