This patch fixes a crash in the libxml2 bindings for Python 3.x
that 'itstool' stumbles upon when processing UTF-8 data:

  https://issues.guix.gnu.org/issue/37468

Patch by Jan Matejek
from <https://bugzilla.opensuse.org/show_bug.cgi?id=1065270>.

--- libxml2-2.9.5.orig/python/libxml.c
+++ libxml2-2.9.5/python/libxml.c
@@ -1620,6 +1620,7 @@ libxml_xmlErrorFuncHandler(ATTRIBUTE_UNU
     PyObject *message;
     PyObject *result;
     char str[1000];
+    unsigned char *ptr = (unsigned char *)str;
 
 #ifdef DEBUG_ERROR
     printf("libxml_xmlErrorFuncHandler(%p, %s, ...) called\n", ctx, msg);
@@ -1636,12 +1637,20 @@ libxml_xmlErrorFuncHandler(ATTRIBUTE_UNU
 	    str[999] = 0;
         va_end(ap);
 
+#if PY_MAJOR_VERSION >= 3
+        /* Ensure the error string doesn't start at UTF8 continuation. */
+        while (*ptr && (*ptr & 0xc0) == 0x80)
+            ptr++;
+#endif
+
         list = PyTuple_New(2);
         PyTuple_SetItem(list, 0, libxml_xmlPythonErrorFuncCtxt);
         Py_XINCREF(libxml_xmlPythonErrorFuncCtxt);
-        message = libxml_charPtrConstWrap(str);
+        message = libxml_charPtrConstWrap(ptr);
         PyTuple_SetItem(list, 1, message);
         result = PyEval_CallObject(libxml_xmlPythonErrorFuncHandler, list);
+        /* Forget any errors caused in the error handler. */
+        PyErr_Clear();
         Py_XDECREF(list);
         Py_XDECREF(result);
     }
9d72d05ed341df9d'>commit</a><a href='/guix/diff/gnu/bootloader/grub.scm?id=a53c6040e4cf15f161a010d39d72d05ed341df9d'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/bootloader/grub.scm'>
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<div class='path'>path: <a href='/guix/log/?id=a53c6040e4cf15f161a010d39d72d05ed341df9d'>root</a>/<a href='/guix/log/gnu?id=a53c6040e4cf15f161a010d39d72d05ed341df9d'>gnu</a>/<a href='/guix/log/gnu/bootloader?id=a53c6040e4cf15f161a010d39d72d05ed341df9d'>bootloader</a>/<a href='/guix/log/gnu/bootloader/grub.scm?id=a53c6040e4cf15f161a010d39d72d05ed341df9d'>grub.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/bootloader/grub.scm?id=a53c6040e4cf15f161a010d39d72d05ed341df9d&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2021-08-29 01:05:26 -0400'>2021-08-29</span></td><td><a href='/guix/commit/gnu/bootloader/grub.scm?id=da4e40948326387d5bcda58783914d5f9ce8b095'>Migrate to the new 'targets' field of bootloader-configuration.</a><span class='msg-avail'>...<span class='msg-tooltip'>The old 'target' field is deprecated; adjust the sources to use the new
'targets' one instead.

* doc/guix-cookbook.texi&lt;target&gt;: Replace by 'targets'.
* gnu/bootloader/grub.scm: Likewise.
* gnu/installer/parted.scm: Likewise.
* gnu/machine/digital-ocean.scm: Likewise.
* gnu/system/examples/asus-c201.tmpl: Likewise
* gnu/system/examples/bare-bones.tmpl: Likewise
* gnu/system/examples/bare-hurd.tmpl: Likewise
* gnu/system/examples/beaglebone-black.tmpl: Likewise
* gnu/system/examples/desktop.tmpl: Likewise
* gnu/system/examples/docker-image.tmpl: Likewise
* gnu/system/examples/lightweight-desktop.tmpl: Likewise
* gnu/system/examples/vm-image.tmpl: Likewise
* gnu/system/examples/yggdrasil.tmpl: Likewise
* gnu/system/hurd.scm: Likewise
* gnu/system/images/hurd.scm: Likewise
* gnu/system/images/novena.scm: Likewise
* gnu/system/images/pine64.scm: Likewise
* gnu/system/images/pinebook-pro.scm: Likewise
* gnu/system/images/rock64.scm: Likewise
* gnu/system/install.scm: Likewise
* gnu/system/vm.scm: Likewise
* gnu/tests.scm: Likewise
* gnu/tests/ganeti.scm: Likewise
* gnu/tests/install.scm: Likewise
* gnu/tests/nfs.scm: Likewise
* gnu/tests/telephony.scm: Likewise
* tests/boot-parameters.scm: Likewise
* tests/system.scm: Likewise
</span></span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2021-04-10 14:11:33 +0200'>2021-04-10</span></td><td><a href='/guix/commit/gnu/bootloader/grub.scm?id=816a5ecdc8286f3c26abfb1f1e7cab04b6b21803'>bootloader: grub: Fix typo in docstring.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/bootloader/grub.scm (install-grub-efi-netboot): Fix typo.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>