hd-rum-translator: do not crash on incorrect use

do not crash on `hd-rum-transcode 8M 5004 -P 8000` (hostname missing
after port specification)

src/hd-rum-translator/hd-rum-translator.cpp

@@ -656,6 +656,11 @@ static int parse_fmt(int argc, char **argv, struct cmdline_parameters *parsed)
         }
     }
 
+    if (argc >= 2 && argv[argc - 2][0] == '-') {
+        fprintf(stderr, "Error: last option on is option '%s', expected hostname\n", argv[argc - 2]);
+        return -1;
+    }
+
     parsed->hosts.resize(parsed->host_count);
     // default values
     for(int i = 0; i < parsed->host_count; ++i) {