[CLN-list] [cppcheck] Member variable 'gcd_result::gcd_degree' is not initialised in the constructor.

Hi, during a check with the static code analysis tool cppcheck of the current git head of cln, the tool discoverd a not initialized member variable of class gcd_result::gcd_degree. Please refer the attached patch that fixes the issue. Best regards from the cppcheck team Ettl Martin