uninitialized variable in decimal-test

[Ben Pfaff]

Hi John.  GCC reports:

    ../tests/math/decimal-test.c: In function ‘canonicalise_string’:
    ../tests/math/decimal-test.c:103:16: error: ‘out’ may be used uninitialized 
in this function [-Werror=maybe-uninitialized]
           *(out+1) = '\0';
                    ^

and I think that I agree with it.  Will you take a look, please?

Thanks,

Ben.