PDFBOX-6085: bugfix skip invisible glyphs when adding compound references

git-svn-id: https://svn.apache.org/repos/asf/pdfbox/trunk@1929280 13f79535-47bb-0310-9956-ffa450edef68

Author: THausherr

fontbox/src/main/java/org/apache/fontbox/ttf/TTFSubsetter.java

@@ -527,7 +527,10 @@ private void addCompoundReferences() throws IOException
                         LOG.debug("Tried skipping {} bytes but skipped only {} bytes",
                                 offset - lastOff, isResult);
                     }
-
+                    if (invisibleGlyphIds.contains(gid))
+                    {
+                        continue;
+                    }
                     byte[] buf = new byte[(int) length];
                     isResult = is.read(buf);