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);
     }
 href='/guix/diff/gnu/tests/pam.scm?id=26638b8e8129aa755586d017677b4cf076bafda6'>diff</a></td><td class='form'><form class='right' method='get' action='/guix/log/gnu/tests/pam.scm'>
<input type='hidden' name='id' value='26638b8e8129aa755586d017677b4cf076bafda6'/><select name='qt'>
<option value='grep'>log msg</option>
<option value='author'>author</option>
<option value='committer'>committer</option>
<option value='range'>range</option>
</select>
<input class='txt' type='search' size='10' name='q' value=''/>
<input type='submit' value='search'/>
</form>
</td></tr></table>
<div class='path'>path: <a href='/guix/log/?id=26638b8e8129aa755586d017677b4cf076bafda6'>root</a>/<a href='/guix/log/gnu?id=26638b8e8129aa755586d017677b4cf076bafda6'>gnu</a>/<a href='/guix/log/gnu/tests?id=26638b8e8129aa755586d017677b4cf076bafda6'>tests</a>/<a href='/guix/log/gnu/tests/pam.scm?id=26638b8e8129aa755586d017677b4cf076bafda6'>pam.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/tests/pam.scm?id=26638b8e8129aa755586d017677b4cf076bafda6&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
 class='left'>Author</th></tr>
<tr><td><span title='2024-04-01 14:09:20 +0200'>2024-04-01</span></td><td><a href='/guix/commit/po/packages/pt_BR.po?id=fa98837b1d9586b9ca7bf77dae22c3bde0fc59b5'>nls: Update translations.</a><span class='msg-avail'>...</span></td><td>Florian Pelz</td></tr>
<tr><td><span title='2023-08-31 21:36:03 +0200'>2023-08-31</span></td><td><a href='/guix/commit/po/packages/pt_BR.po?id=57ab9536db20f98a36aeb25972137fbd752686cc'>nls: Update translations.</a></td><td>Florian Pelz</td></tr>
<tr><td><span title='2023-05-31 17:23:21 +0200'>2023-05-31</span></td><td><a href='/guix/commit/po/packages/pt_BR.po?id=8e9e6a6482f3ba98d1cdcad344ee488e8751fee7'>nls: Update translations.</a><span class='msg-avail'>...</span></td><td>Florian Pelz</td></tr>