Merge pull request #12365 from Snuffleupagus/forbid-DecodeStream.length

Ensure that the `length` property won't be *accidentally* accessed on a `DecodeStream`-instance

src/core/stream.js

@@ -167,6 +167,11 @@ var DecodeStream = (function DecodeStreamClosure() {
   }
 
   DecodeStream.prototype = {
+    // eslint-disable-next-line getter-return
+    get length() {
+      unreachable("Should not access DecodeStream.length");
+    },
+
     get isEmpty() {
       while (!this.eof && this.bufferLength === 0) {
         this.readBlock();