Make base prefix sigils error out if no number following Prefix sigils (0x, %, &, @, $) were parsing to 0 if there was no number following the prefix. Make parsing fail if that is the case. Note that in a couple of obscure cases, it may give "undefined symbol" rather than "bad operand" due to some interactions with other unfortunate features of the source format.

\.exe$
\.o$
\.d$
\.a$
~$
\.orig$
/lwbasic$
/lwlink$
/lwobjdump$
/lwar$
/lwasm$
/lwcc/lwcc$
/lwcc/lwcpp$