Skip empty classes in pulse len calculation.

app.c

@@ -120,6 +120,7 @@ uint32_t search_coherent_signal(RawSamplesBuffer *s, uint32_t idx) {
      * for visualization. */
     for (int j = 0; j < SEARCH_CLASSES; j++) {
         for (int level = 0; level < 2; level++) {
+            if (classes[j].dur[level] == 0) continue;
             if (s->short_pulse_dur == 0 ||
                 s->short_pulse_dur > classes[j].dur[level])
             {