float.c: correct exponent capping
float.c: correct exponent capping

Actually enforce the exponent capping, as opposed to only enforcing it
to within a factor of 10.  Furthermore, continue to scan the string in
order to check for invalid characters.

Finally, 16384 is too tight of a bound for a binary exponent: it's a
tight bound, but the shift added due to the digit string can move the
cap into the active region (±16383).  Thus, change it to 20000 to be
on the safe side.

projedi/nasm,Distrotech/nasm,Distrotech/nasm,techkey/nasm,techkey/nasm,techkey/nasm,projedi/nasm,projedi/nasm,Distrotech/nasm,techkey/nasm,Distrotech/nasm,turingstudio/nasm,letolabs/nasm,turingstudio/nasm,turingstudio/nasm,letolabs/nasm,turingstudio/nasm,letolabs/nasm,projedi/nasm,projedi/nasm,techkey/nasm