Fixed integer rollover bug in toxav.

toxav/toxav.c

@@ -151,7 +151,11 @@ uint32_t toxav_do_interval(ToxAv *av)
             rc = MIN(av->calls[i].cs->audio_decoder_frame_duration, rc);
         }
 
-    return rc - av->avgdectms;
+    if (rc < av->avgdectms) {
+        return 0;
+    } else {
+        return rc - av->avgdectms;
+    }
 }
 
 void toxav_do(ToxAv *av)