fix -Wunused-result warning when calling getcwd()
fix -Wunused-result warning when calling getcwd()

Fix this warning:

    lnav_log.cc: In function ‘void log_host_info()’:
    lnav_log.cc:185:29: warning: ignoring return value of ‘char* getcwd(char*, size_t)’, declared with attribute warn_unused_result [-Wunused-result]
         getcwd(cwd, sizeof(cwd));
                                 ^

sureshsundriyal/lnav,tstack/lnav,sureshsundriyal/lnav,tstack/lnav,sureshsundriyal/lnav,tstack/lnav,sureshsundriyal/lnav,tstack/lnav