Print help when calling cct without arguments

Previously when calling cct without any arguments the following
message would be presented to the user:

    cct: Bad transformation arguments - ((null))
        'cct -h' for help

With this change the help instructions are returned instead.

src/cct.c

@@ -165,7 +165,7 @@ int main(int argc, char **argv) {
     if (0==o)
         return 0;
 
-    if (opt_given (o, "h")) {
+    if (opt_given (o, "h") || argc==1) {
         printf (usage, o->progname);
         return 0;
     }