When the call to erl_scan succeeded returning more than one token,
for example "123_", the unexpected success was not detected.

In cases such as "123a45", the scanner did not report an error, instead
returning two tokens '123' and 'a45'. The splitting point depends on the
base, so e.g., "16#12fg34" was scanned as '16#12f' and 'g34'. This change
makes the scanner reject numbers immediately followed by a name character.