Bug #920575: Add a workaround for GNU libc nl_langinfo()'s returning NULL.

(Reported by Matthias Klose)

Misc/NEWS

@@ -193,6 +193,9 @@ Core and builtins
 Extension modules
 -----------------
 
+- Bug #920575: A problem that _locale module segfaults on
+  nl_langinfo(ERA) caused by GNU libc's illegal NULL return is fixed.
+
 - array objects now support the copy module.  Also, their resizing
   scheme has been updated the same as for list objects.  The improves
   the performance (speed and memory usage) of append() operations.

Modules/_localemodule.c

@@ -592,8 +592,12 @@ PyLocale_nl_langinfo(PyObject* self, PyObject* args)
     }
 #endif
     for (i = 0; langinfo_constants[i].name; i++)
-	    if (langinfo_constants[i].value == item)
-		    return PyString_FromString(nl_langinfo(item));
+        if (langinfo_constants[i].value == item) {
+            /* Check NULL as a workaround for GNU libc's returning NULL
+               instead of an empty string for nl_langinfo(ERA).  */
+            const char *result = nl_langinfo(item);
+            return PyString_FromString(result != NULL ? result : "");
+        }
     PyErr_SetString(PyExc_ValueError, "unsupported langinfo constant");
     return NULL;
 }