[3.12] gh-114286: Fix maybe-uninitialized warning in Modules/_io/fileio.c (GH-114287) (GH-114288)

(cherry picked from commit 05e4720)

Co-authored-by: Nikita Sobolev <[email protected]>

Author: miss-islington

Modules/_io/fileio.c

@@ -153,7 +153,7 @@ _io_FileIO_close_impl(fileio *self, PyTypeObject *cls)
         return res;
     }
 
-    PyObject *exc;
+    PyObject *exc = NULL;
     if (res == NULL) {
         exc = PyErr_GetRaisedException();
     }