#4841: Fix FileIO constructor to honor closefd when called repeatedly

Patch by Victor Stinner.
diff --git a/Modules/_io/fileio.c b/Modules/_io/fileio.c
index d5b03ee..c51d697 100644
--- a/Modules/_io/fileio.c
+++ b/Modules/_io/fileio.c
@@ -227,9 +227,13 @@
 
     assert(PyFileIO_Check(oself));
     if (self->fd >= 0) {
-        /* Have to close the existing file first. */
-        if (internal_close(self) < 0)
-            return -1;
+        if (self->closefd) {
+            /* Have to close the existing file first. */
+            if (internal_close(self) < 0)
+                return -1;
+        }
+        else
+            self->fd = -1;
     }
 
     if (!PyArg_ParseTupleAndKeywords(args, kwds, "O|si:fileio",