When compacting the receive buffer don't copy unused buffer space

When compacting the receive buffer, we should only copy the bytes
between _rQi and _rQlen (the index of the first unread byte, and the
next write position).

Previously, we copied everything for _rQi up untill the end of the
buffer.

kasmweb/core/websock.js

@@ -247,12 +247,12 @@ export default class Websock {
         if (resizeNeeded) {
             const old_rQbuffer = this._rQ.buffer;
             this._rQ = new Uint8Array(this._rQbufferSize);
-            this._rQ.set(new Uint8Array(old_rQbuffer, this._rQi));
+            this._rQ.set(new Uint8Array(old_rQbuffer, this._rQi, this._rQlen - this._rQi));
         } else {
             if (ENABLE_COPYWITHIN) {
-                this._rQ.copyWithin(0, this._rQi);
+                this._rQ.copyWithin(0, this._rQi, this._rQlen);
             } else {
-                this._rQ.set(new Uint8Array(this._rQ.buffer, this._rQi));
+                this._rQ.set(new Uint8Array(this._rQ.buffer, this._rQi, this._rQlen - this._rQi));
             }
         }