PDFBOX-5908: improve / simplify / clarify code as suggested by Michael Klink

git-svn-id: https://svn.apache.org/repos/asf/pdfbox/trunk@1922178 13f79535-47bb-0310-9956-ffa450edef68

Author: THausherr

pdfbox/src/main/java/org/apache/pdfbox/filter/Filter.java

@@ -270,13 +270,13 @@ public static RandomAccessRead decode(InputStream encoded, List<Filter> filterLi
             }
             // we don't know the size of the decoded stream, just estimate a 4 times bigger size than the encoded stream
             // use the estimated stream size as chunk size, use the default chunk size as limit to avoid to big values
-            if (length >= RandomAccessReadBuffer.DEFAULT_CHUNK_SIZE_4KB / 4)
+            if (length <= 0 || length >= RandomAccessReadBuffer.DEFAULT_CHUNK_SIZE_4KB / 4)
             {
                 length = RandomAccessReadBuffer.DEFAULT_CHUNK_SIZE_4KB;
             }
             else
             {
-                length = Math.min(length << 2, RandomAccessReadBuffer.DEFAULT_CHUNK_SIZE_4KB);
+                length = length * 4;
             }
             randomAccessWriteBuffer = new RandomAccessReadWriteBuffer((int) length);
             output = new RandomAccessOutputStream(randomAccessWriteBuffer);