Merge pull request #6386 from Snuffleupagus/Parser_makeFilter-warn-on-empty-stream

Add a warning when we encounter an empty stream in `Parser_makeFilter`

src/core/parser.js

@@ -528,6 +528,7 @@ var Parser = (function ParserClosure() {
     },
     makeFilter: function Parser_makeFilter(stream, name, maybeLength, params) {
       if (stream.dict.get('Length') === 0 && !maybeLength) {
+        warn('Empty "' + name + '" stream.');
         return new NullStream(stream);
       }
       try {