Otherwise we get a CLANG_WARNING due accessing garbage.

Covscan report:
 > spice-vdagent-0.19.0/src/vdagent/vdagent.c:471:9: warning: 1st function call argument is an uninitialized value
 > #        execvp(orig_argv[0], orig_argv);
 > #        ^      ~~~~~~~~~~~~
 > spice-vdagent-0.19.0/src/vdagent/vdagent.c:421:24: note: Storing uninitialized value
 > #    char **orig_argv = g_memdup(argv, sizeof(char*) * (argc+1));
 > #                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 > spice-vdagent-0.19.0/src/vdagent/vdagent.c:434:9: note: Assuming 'error' is equal to NULL
 > #    if (error != NULL) {
 > #        ^~~~~~~~~~~~~
 > spice-vdagent-0.19.0/src/vdagent/vdagent.c:434:5: note: Taking false branch
 > #    if (error != NULL) {
 > #    ^
 > spice-vdagent-0.19.0/src/vdagent/vdagent.c:442:9: note: Assuming 'portdev' is not equal to NULL
 > #    if (portdev == NULL)
 > #        ^~~~~~~~~~~~~~~
 > spice-vdagent-0.19.0/src/vdagent/vdagent.c:442:5: note: Taking false branch
 > #    if (portdev == NULL)
 > #    ^
 > spice-vdagent-0.19.0/src/vdagent/vdagent.c:445:9: note: Assuming 'vdagentd_socket' is not equal to NULL
 > #    if (vdagentd_socket == NULL)
 > #        ^~~~~~~~~~~~~~~~~~~~~~~
 > spice-vdagent-0.19.0/src/vdagent/vdagent.c:445:5: note: Taking false branch
 > #    if (vdagentd_socket == NULL)
 > #    ^
 > spice-vdagent-0.19.0/src/vdagent/vdagent.c:448:30: note: Assuming 'do_daemonize' is 0
 > #    openlog("spice-vdagent", do_daemonize ? LOG_PID : (LOG_PID | LOG_PERROR),
 > #                             ^~~~~~~~~~~~
 > spice-vdagent-0.19.0/src/vdagent/vdagent.c:448:30: note: '?' condition is false
 > spice-vdagent-0.19.0/src/vdagent/vdagent.c:451:9: note: Assuming the condition is false
 > #    if (!g_file_test(portdev, G_FILE_TEST_EXISTS)) {
 > #        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 > spice-vdagent-0.19.0/src/vdagent/vdagent.c:451:5: note: Taking false branch
 > #    if (!g_file_test(portdev, G_FILE_TEST_EXISTS)) {
 > #    ^
 > spice-vdagent-0.19.0/src/vdagent/vdagent.c:457:9: note: Assuming 'do_daemonize' is 0
 > #    if (do_daemonize)
 > #        ^~~~~~~~~~~~
 > spice-vdagent-0.19.0/src/vdagent/vdagent.c:457:5: note: Taking false branch
 > #    if (do_daemonize)
 > #    ^
 > spice-vdagent-0.19.0/src/vdagent/vdagent.c:468:9: note: Assuming 'version_mismatch' is not equal to 0
 > #    if (version_mismatch) {
 > #        ^~~~~~~~~~~~~~~~
 > spice-vdagent-0.19.0/src/vdagent/vdagent.c:468:5: note: Taking true branch
 > #    if (version_mismatch) {
 > #    ^
 > spice-vdagent-0.19.0/src/vdagent/vdagent.c:471:9: note: 1st function call argument is an uninitialized value
 > #        execvp(orig_argv[0], orig_argv);
 > #        ^      ~~~~~~~~~~~~
 > #  469|           syslog(LOG_INFO, "Version mismatch, restarting");
 > #  470|           sleep(1);
 > #  471|->         execvp(orig_argv[0], orig_argv);
 > #  472|       }
 > #  473|

Signed-off-by: Victor Toso <victortoso@redhat.com>
Acked-by: Uri Lublin <uril@redhat.com>