Do not include zero-length delays in output

This would cause lockup in ATtiny-playtune and output can be significantly
shorter without zero-length delays.

See http://www.mariopiano.com/Mario-Sheet-Music-Overworld-Main-Theme.mid

miditones.c

@@ -1225,6 +1225,7 @@ This is not unlike multiway merging used for tape sorting algoritms in the 50's!
             unsigned long long temp;
             temp = ((unsigned long long) delta_time * tempo) / ticks_per_beat;
             delta_msec = temp / 1000;   // get around LCC compiler bug
+            if (delta_msec) {
               if (loggen)
                  fprintf (logfile, "->Delay %ld msec (%ld ticks)\n", delta_msec, delta_time);
               if (delta_msec > 0x7fff)
@@ -1239,6 +1240,7 @@ This is not unlike multiway merging used for tape sorting algoritms in the 50's!
                  outfile_items (2);
               }
             }
+         }
          timenow = earliest_time;
 
          /*  If this track event is "set tempo", just change the global tempo.