GUI: fix per-chan osc visual glitch when stopping

src/engine/engine.cpp

@@ -2441,6 +2441,16 @@ void DivEngine::stop() {
       }
     }
   }
+
+  // reset all chan oscs
+  for (int i=0; i<chans; i++) {
+    DivDispatchOscBuffer* buf=disCont[dispatchOfChan[i]].dispatch->getOscBuffer(dispatchChanOfChan[i]);
+    if (buf!=NULL) {
+      memset(buf->data,0,65536*sizeof(short));
+      buf->needle=0;
+      buf->readNeedle=0;
+    }
+  }
   BUSY_END;
 }