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);
     }
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<tr><td><span title='2019-01-26 14:46:40 +0100'>2019-01-26</span></td><td><a href='/guix/commit/gnu/packages/datastructures.scm?id=c9e75159706368be7b0b9d8a8fe33dc2786e37a7'>gnu: uthash: Use INVOKE.</a><span class='msg-avail'>...</span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2019-01-26 14:46:05 +0100'>2019-01-26</span></td><td><a href='/guix/commit/gnu/packages/datastructures.scm?id=d1293d426dcfb711a8c156ff66b7cdc93ff32fef'>gnu: uthash: Fetch sources via git.</a><span class='msg-avail'>...</span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2019-01-19 00:03:23 +0100'>2019-01-19</span></td><td><a href='/guix/commit/gnu/packages/datastructures.scm?id=3a1d01ca324c9cba55a33fb1f0d9007cc01e65da'>gnu: liburcu: Update to 0.10.2.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2019-01-19 00:03:14 +0100'>2019-01-19</span></td><td><a href='/guix/commit/gnu/packages/datastructures.scm?id=4dfda8dce065c199216b452fe48ac73405893a47'>gnu: liburcu: Use HTTPS home page.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2019-01-07 11:56:14 +0100'>2019-01-07</span></td><td><a href='/guix/commit/gnu/packages/datastructures.scm?id=ad6f13308b1b3ee38ef76482bc597d9a9e1a31c2'>gnu: Add sdsl-lite.</a><span class='msg-avail'>...</span></td><td>Ricardo Wurmus</td></tr>
<tr><td><span title='2018-11-10 23:33:46 +0100'>2018-11-10</span></td><td><a href='/guix/commit/gnu/packages/datastructures.scm?id=9d466489cdbbfb2097ec3e211351d7b34fb70b60'>gnu: Add marisa.</a><span class='msg-avail'>...</span></td><td>Meiyo Peng</td></tr>
<tr><td><span title='2018-01-24 15:47:52 +0100'>2018-01-24</span></td><td><a href='/guix/commit/gnu/packages/datastructures.scm?id=8f4bf6a99065f836858c42ebcd2ee8a6c4482c65'>gnu: liburcu: Update to 0.10.1.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2017-12-12 05:12:13 +0100'>2017-12-12</span></td><td><a href='/guix/commit/gnu/packages/datastructures.scm?id=cc3ac162c558a51c90b76b84b081a15e28d0baad'>gnu: Add uthash.</a><span class='msg-avail'>...</span></td><td>Tobias Geerinckx-Rice</td></tr>