patch 8.1.1346: error for Python exception does not show useful info

Problem:    Error for Python exception does not show useful info.
Solution:   Show the last line instead of the first one. (Ben Jackson,
            closes #4381)
diff --git a/src/if_py_both.h b/src/if_py_both.h
index 4e1a42a..cc0450c 100644
--- a/src/if_py_both.h
+++ b/src/if_py_both.h
@@ -412,6 +412,8 @@
 
     Py_BEGIN_ALLOW_THREADS
     Python_Lock_Vim();
+    if (error)
+	emsg_severe = TRUE;
     writer((writefn)(error ? emsg : msg), (char_u *)str, len);
     Python_Release_Vim();
     Py_END_ALLOW_THREADS