Bug fix.

There are checks to make sure that if a number is not in decimal, it
does not have an exponent marker. Unfortunately, the code that detects
an exponent marker, will only do so if the number is not a decimal
number. This means numbers in the number #x5l0 the 'l' would not be
considered an exponent marker. The good news is that any of these
cases would have eventually been caught by parse-integer, since it
would be passed the exponent marker, signaling an error because it is
not a digit in the given radix.

To fix this, the code the detects an exponent marker will run if the
character is not a digit in the radix as opposed to running only when
the radix is decimal.