Issue #28410: Added _PyErr_FormatFromCause() -- the helper for raising
new exception with setting current exception as __cause__.

_PyErr_FormatFromCause(exception, format, args...) is equivalent to Python

    raise exception(format % args) from sys.exc_info()[1]
diff --git a/Objects/unicodeobject.c b/Objects/unicodeobject.c
index adeec8c..80e6cf2 100644
--- a/Objects/unicodeobject.c
+++ b/Objects/unicodeobject.c
@@ -3835,13 +3835,10 @@
                                 Py_FileSystemDefaultEncodeErrors);
 #ifdef MS_WINDOWS
         if (!res && PyErr_ExceptionMatches(PyExc_UnicodeDecodeError)) {
-            PyObject *exc, *val, *tb;
-            PyErr_Fetch(&exc, &val, &tb);
-            PyErr_Format(PyExc_RuntimeError,
-                "filesystem path bytes were not correctly encoded with '%s'. " \
+            _PyErr_FormatFromCause(PyExc_RuntimeError,
+                "filesystem path bytes were not correctly encoded with '%s'. "
                 "Please report this at http://bugs.python.org/issue27781",
                 Py_FileSystemDefaultEncoding);
-            _PyErr_ChainExceptions(exc, val, tb);
         }
 #endif
         return res;