Fix issue reading from large streams

PregReplaceFilterStream didn't implement eof(), which caused an
issue using stream_get_contents on a guzzle resource created out
of the stream

zbateson/mail-mime-parser#84
zbateson/mail-mime-parser#87

src/PregReplaceFilterStream.php

@@ -46,6 +46,16 @@ public function __construct(StreamInterface $stream, $pattern, $replacement)
         $this->buffer = new BufferStream();
     }
 
+    /**
+     * Returns true if the end of stream has been reached.
+     *
+     * @return boolean
+     */
+    public function eof()
+    {
+        return ($this->buffer->eof() && $this->stream->eof());
+    }
+
     /**
      * Not supported by PregReplaceFilterStream
      *