Fix a memory leak in dhclient

[trix_juniper.net]

Summary

clparse.c parse_client_lease_statement
When there is an error parsing, call free_client_lease to free the memory assigned to the variable 'lease' before returning early.

Test Plan

Use clang's static analyzer, scan-build, to find the problem and later to show resolution.

[ngie]

Thank you for the submission! I'll take care of the other memory leaks noted by Coverity.