IsValidXref() no will no longer check if it's inside of a stream beyong an EOF symbol.

Author: mlaukala

src/PdfSharp/Pdf.IO/Parser.cs

@@ -1088,14 +1088,17 @@ private bool IsValidXref()
 				content += _lexer.ReadRawString(content_pos, read_length);
 
 				int ss = content.IndexOf("stream", StringComparison.Ordinal);
+				int eof = content.IndexOf("%%EOF", StringComparison.Ordinal);
 				int es = content.IndexOf("endstream", StringComparison.Ordinal);
 
-				if (ss < es)
+				int s = Math.Min(ss, eof);
+
+				if (s < es)
 				{
 					// Not inside of stream
 					break;
 				}
-				else if (es != -1 && ss > es)
+				else if (s > es)
 				{
 					// inside of stream
 					return false;