Handle correctly _Py_fopen() error: don't replace the exception

Modules/zipimport.c

@@ -736,6 +736,7 @@ read_directory(PyObject *archive_obj)
 
     fp = _Py_fopen(archive_obj, "rb");
     if (fp == NULL) {
+        if (!PyErr_Occurred())
             PyErr_Format(ZipImportError, "can't open Zip file: '%U'", archive_obj);
         return NULL;
     }
@@ -909,6 +910,7 @@ get_data(PyObject *archive, PyObject *toc_entry)
 
     fp = _Py_fopen(archive, "rb");
     if (!fp) {
+        if (!PyErr_Occurred())
             PyErr_Format(PyExc_IOError,
                "zipimport: can not open file %U", archive);
         return NULL;