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='2020-07-12 23:08:15 +0200'>2020-07-12</span></td><td><a href='/guix/commit/gnu/packages/synergy.scm?id=b0e7b6992f3f845e83cfbca4d700b51dba50b4d5'>gnu: Remove ".git" from "https://github/…/….git".</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2020-07-03 14:06:42 -0500'>2020-07-03</span></td><td><a href='/guix/commit/gnu/packages/synergy.scm?id=2ca4ae2993e20a1415fa25acf8fd6b993ee48c18'>gnu: Update synergy to 1.11.1.</a><span class='msg-avail'>...</span></td><td>Eric Bavier</td></tr>
<tr><td><span title='2020-04-03 18:04:38 +0200'>2020-04-03</span></td><td><a href='/guix/commit/gnu/packages/synergy.scm?id=ba66eec741a9fbddd74eb7fc54d2c53888ace5b7'>gnu: synergy: Fix build failure.</a><span class='msg-avail'>...</span></td><td>Marius Bakke</td></tr>
<tr><td><span title='2020-01-17 17:34:35 -0600'>2020-01-17</span></td><td><a href='/guix/commit/gnu/packages/synergy.scm?id=b410c0355aeb8a282a2ee6204676efa8fe77b67a'>gnu: synergy: Update to 1.11.0.</a><span class='msg-avail'>...</span></td><td>Eric Bavier</td></tr>