Fix a bug whereby 'mformat' could end up passing uninitialized bytes
to write(2).  This could be reproduced with:

  mformat -C -f 1440 -L 16  -N 77777777 -i  /tmp/x ::

where the output of /tmp/x would be non-deterministic.

Patch by Ludovic Courtès <ludo@gnu.org>.

--- mtools-4.0.23/mformat.c	2019-04-21 00:12:01.496116195 +0200
+++ mtools-4.0.23/mformat.c	2019-04-21 00:12:36.675967157 +0200
@@ -927,6 +927,7 @@ void mformat(int argc, char **argv, int
 	
 	char *endptr;
 
+	memset(&boot.bytes, '\0', sizeof boot);
 	hs = hs_set = 0;
 	argtracks = 0;
 	argheads = 0;

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<tr><td><span title='2016-05-30 20:13:24 +0300'>2016-05-30</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=1f521b7055a464439774332f1a69ed31b565715f'>gnu: id3lib: Fix CVE-2007-4460.</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2016-05-27 11:37:53 +0300'>2016-05-27</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=ea3d5291ccad5b78a0edafc986366633eb60d2fe'>gnu: eyed3: Update to 0.7.9.</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2016-05-27 11:37:53 +0300'>2016-05-27</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=1a847b708dfa13c5ea231c6fc729db0088079925'>gnu: mpc123: Use 'modify-phases'.</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2016-05-27 11:37:53 +0300'>2016-05-27</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=d1cd67af5dc305572b018e4dd46eb7d035244dda'>gnu: mpc123: Add new source location.</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2016-04-14 10:38:21 +0300'>2016-04-14</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=fc1adab1487e5ea3c5f6341263df14414ba4e784'>gnu: packages: Use 'search-patches' everywhere.</a><span class='msg-avail'>...</span></td><td>Alex Kost</td></tr>
<tr><td><span title='2015-12-06 23:12:12 +0100'>2015-12-06</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=f8f8897f7ef7dffb0ad5a68a7fd5106e2c61c48b'>gnu: mp3info: Update URL.</a><span class='msg-avail'>...</span></td><td>Alex Vong</td></tr>
<tr><td><span title='2015-11-25 17:01:02 +0100'>2015-11-25</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=13ef3e997b469ab605d29fc91131c0330cb5ec21'>gnu: Add eyeD3.</a><span class='msg-avail'>...</span></td><td>Leo Famulari</td></tr>
<tr><td><span title='2015-10-01 19:39:34 +0300'>2015-10-01</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=9e125175fc65f72d2bf9724905b3cbe0a467b6c4'>gnu: mpg123: Update to 1.22.4.</a><span class='msg-avail'>...</span></td><td>Efraim Flashner</td></tr>
<tr><td><span title='2015-08-29 01:25:08 +0200'>2015-08-29</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=96c462105627569ae4b82cdc0e0059806f855ba6'>gnu: Use 'install-file' instead of 'mkdir-p' and 'copy-file' in obvious cases.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2015-07-24 21:16:29 +0200'>2015-07-24</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=d0dfc06683c868e48ee85213909e4013db94e221'>gnu: ripperX: Update to 2.8.0.</a><span class='msg-avail'>...</span></td><td>Andreas Enge</td></tr>
<tr><td><span title='2015-07-21 02:05:20 -0400'>2015-07-21</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=c0eac5a86246a2c8eb4fe3177a64cfc9687cf5e0'>gnu: libmad: Apply fixes for ARMv7 Thumb, etc.</a><span class='msg-avail'>...</span></td><td>Mark H Weaver</td></tr>
<tr><td><span title='2015-07-18 13:05:01 +0300'>2015-07-18</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=e881752c39d455a249731a4e81e64d86f50afc34'>gnu packages: Clean up synopses and descriptions.</a><span class='msg-avail'>...</span></td><td>Alex Kost</td></tr>
<tr><td><span title='2015-06-21 14:08:39 -0400'>2015-06-21</span></td><td><a href='/guix/commit/gnu/packages/mp3.scm?id=194782a881fbcf6ac47122a0e85fbe5b69c6af58'>gnu: lame: Build with gcc-4.8 on i686.</a><span class='msg-avail'>...</span></td><td>Mark H Weaver</td></tr>