info hangs in text_buffer_iconv() on malformed input file

[Nathaniel Beaver]

Steps to reproduce:

info -f reproduce_bug.info

Expected behavior:

info exits with an error.

Actual behavior:

info stuck in an infinite loop

Comments:

The bug does not seem to be reproducible with info version 6.5. It is 
reproducible with the latest git revision; I'm not sure when it was 
introduced.

The file was generated with afl-fuzz and then hand-edited. The only 
addition to the original file is a misplaced index tag:

^@^H[index^@^H]

When run on the gzipped version, the result is a segmentation fault in 
utf8_internal_loop() instead of an infinite loop in text_buffer_iconv().

Sincerely,

Nathaniel Beaver

P.S. Version information:

$ git describe --tags
texinfo-6.6-700-g97eb358ee3
$ git rev-parse HEAD
97eb358ee34966dd1dbc80a78bd5bac77748e112
$ info/ginfo --version
info (GNU texinfo) 6.7dev

Copyright (C) 2019 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later 
<http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

address-sanitizer.txt
Description: Text document

gdb.txt
Description: Text document

gdb-sigsegv.txt
Description: Text document

original.info
Description: application/gnuinfo

original.info.gz
Description: application/gzip

reproduce_bug.info
Description: application/gnuinfo

reproduce_bug.info.gz
Description: application/gzip

valgrind_1635_1.txt
Description: Text document