Fix CVE-2017-16844:

https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2017-16844
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=876511

Patch copied from Debian procmail package 3.22-26:

http://http.debian.net/debian/pool/main/p/procmail/procmail_3.22-26.debian.tar.xz

From: Santiago Vila <sanvila@debian.org>
Subject: Fix heap-based buffer overflow in loadbuf()
Bug-Debian: http://bugs.debian.org/876511
X-Debian-version: 3.22-26

--- a/src/formisc.c
+++ b/src/formisc.c
@@ -103,7 +103,7 @@
 }
 							    /* append to buf */
 void loadbuf(text,len)const char*const text;const size_t len;
-{ if(buffilled+len>buflen)			  /* buf can't hold the text */
+{ while(buffilled+len>buflen)			  /* buf can't hold the text */
      buf=realloc(buf,buflen+=Bsize);
   tmemmove(buf+buffilled,text,len);buffilled+=len;
 }
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<tr><td><span title='2019-06-25 17:22:11 +0200'>2019-06-25</span></td><td><a href='/guix/commit/gnu/packages/mc.scm?id=59b98b48475fe3deb8b356872913ae4b8bbd4e7f'>gnu: mc: Update to 4.8.23.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2019-03-18 15:05:08 +0100'>2019-03-18</span></td><td><a href='/guix/commit/gnu/packages/mc.scm?id=47956fa0c24efcdcba3493f0231c30e9a39ec7df'>Correct name and email address for ng0.</a><span class='msg-avail'>...</span></td><td>ng0</td></tr>
<tr><td><span title='2019-02-27 15:48:50 +0100'>2019-02-27</span></td><td><a href='/guix/commit/gnu/packages/mc.scm?id=0257294a61fac3325505769bd1ef9b3cd7e646b7'>gnu: mc: Update to 4.8.22.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2018-03-20 17:17:58 +0100'>2018-03-20</span></td><td><a href='/guix/commit/gnu/packages/mc.scm?id=4a78fd4617908546be15d2c101f5cab512c71f8e'>Correct name and Email for ng0.</a><span class='msg-avail'>...</span></td><td>ng0</td></tr>
<tr><td><span title='2018-02-08 05:01:41 +0100'>2018-02-08</span></td><td><a href='/guix/commit/gnu/packages/mc.scm?id=b2d00af723b900c6db7d6db5c5f5b20e9955840b'>gnu: mc: Substitute more FHS file names.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
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<tr><td><span title='2018-01-16 14:30:17 +0100'>2018-01-16</span></td><td><a href='/guix/commit/gnu/packages/mc.scm?id=10db64e1b0508100395ff67f19e394f9b45912fa'>gnu: mc: Use HTTPS for home page.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2017-11-19 12:13:43 +0200'>2017-11-19</span></td><td><a href='/guix/commit/gnu/packages/mc.scm?id=c146314566b969d65d52621dec32bde0824f1207'>Update email address for ng0.</a></td><td>ng0</td></tr>