Fix a bug in fmpq_poly_gcd reported by Srajan Garg.
Fix a bug in fmpq_poly_gcd reported by Srajan Garg.

dsroche/flint2,fredrik-johansson/flint2,jpflori/flint2,wbhart/flint2,jpflori/flint2,fredrik-johansson/flint2,dsroche/flint2,jpflori/flint2,dsroche/flint2,dsroche/flint2,fredrik-johansson/flint2,jpflori/flint2,wbhart/flint2,wbhart/flint2