gh-151814: Fix unbounded memory growth from repeated empty writes to io.TextIOWrapper

[StanFromIreland]

• Issue: Runaway memory use when repeatedly printing empty string #151814

[StanFromIreland]

Git seems to render the diff poorly, locally I see with -w (--ignore-all-space):

$ git show -w HEAD -- Modules/_io/textio.c
commit c6b5163133619febd0fbe8c327e52399b1a54ffd (HEAD -> textio-acc, origin/textio-acc)
Author: Stan Ulbrych <stan@python.org>
Date:   Sat Jun 20 21:16:54 2026 +0100

    Fix unbounded memory growth from repeated empty writes to io.TextIOWrapper

diff --git a/Modules/_io/textio.c b/Modules/_io/textio.c
index 24e08cec88f..5b2a20a30c2 100644
--- a/Modules/_io/textio.c
+++ b/Modules/_io/textio.c
@@ -1820,6 +1820,7 @@ _io_TextIOWrapper_write_impl(textio *self, PyObject *text)
         }
     }
 
+    if (bytes_len > 0) {
         if (self->pending_bytes == NULL) {
             assert(self->pending_bytes_count == 0);
             self->pending_bytes = b;
@@ -1846,6 +1847,11 @@ _io_TextIOWrapper_write_impl(textio *self, PyObject *text)
         }
 
         self->pending_bytes_count += bytes_len;
+    }
+    else {
+        Py_DECREF(b);
+    }
+
     if (self->pending_bytes_count >= self->chunk_size || needflush ||
         text_needflush) {
         if (_textiowrapper_writeflush(self) < 0)