An local var `l` in gmtls_construct_client_certificate is uninitialized,
which leads to an cert length mismatch error.
GMTLS handshake using SM2-WITH-SMS4-SM3 cipher suite will be failed due
to this issue.
My editor automatically removed some trailing spaces when I fixed this
bug. So some lines modified in `statem_gmtls.c` are insignificant.
Please ignore them.