mgcp-client: Fix regression checking null ptrA recent patch introduced a bug checking incorrectly for null ptr.Related: Coverity CID#445417Related: Coverity CID#445418Fixes: e6ef4e7484a132cce812396c776f7ab2a291cf8eChange-Id: I1a458a34376851aec73c14a658cccd6132a5eb6c