Fix segv in CPDF_DataAvail::CheckRoot() when /Root object is a string.

testing/tools/fixup_pdf_template.py

 #!/usr/bin/env python
 # Copyright 2014 The PDFium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """Expands a hand-written PDF testcase (template) into a valid PDF file.
 
 There are several places in a PDF file where byte-offsets are required. This
 script replaces {{name}}-style variables in the input with calculated results
 
   {{header}}     - expands to the header comment required for PDF files.
   {{xref}}       - expands to a generated xref table, noting the offset.
   {{startxref}   - expands to a startxref directive followed by correct offset.
   {{object x y}} - expands to |x y obj| declaration, noting the offset."""
 
 import optparse
 import os
 import re
 import sys
 
 class TemplateProcessor:
   HEADER_TOKEN =  '{{header}}'
   HEADER_REPLACEMENT = '%PDF-1.7\n%\xa0\xf2\xa4\xf4'
 
   XREF_TOKEN = '{{xref}}'
   XREF_REPLACEMENT = 'xref\n%d %d\n'
-  XREF_REPLACEMENT_N = '%010d %05d n\n'
-  XREF_REPLACEMENT_F = '0000000000 65536 f\n'
+
+  # XREF rows must be exactly 20 bytes - space required.
+  XREF_REPLACEMENT_N = '%010d %05d n \n'
+  XREF_REPLACEMENT_F = '0000000000 65535 f \n'
 
   STARTXREF_TOKEN= '{{startxref}}'
   STARTXREF_REPLACEMENT = 'startxref\n%d'
 
   OBJECT_PATTERN = r'\{\{object\s+(\d+)\s+(\d+)\}\}'
   OBJECT_REPLACEMENT = r'\1 \2 obj'
 
   def __init__(self):
     self.offset = 0
     self.xref_offset = 0
@@ skipping 41 matching lines @@
   except IOError:
     print >> sys.stderr, 'failed to process %s' % input_filename
 
 def main():
   for arg in sys.argv[1:]:
     expand_file(arg)
   return 0
 
 if __name__ == '__main__':
   sys.exit(main())