avcenc: Make sure that "avcenc --help" works as intended

The --help option is handled by the normal argument parsing loop
below, but that is only invoked if argc > 2.

Change-Id: Icff3625412c340565c062628f2657c41db73068e

test/encoder/main.c

@@ -2088,6 +2088,11 @@ int main(int argc, char *argv[])
     }
     else if(argc == 2)
     {
+        if (!strcmp(argv[1], "--help"))
+        {
+            print_usage();
+            exit(-1);
+        }
         strcpy(ac_cfg_fname, argv[1]);
     }