[libadwaita] preferences-window: plug leak in make_comparable()

[Alexander Mikhaylenko <alexm src gnome org>]

commit 157aecac7b04b04b989da7bd763911ccfd498452
Author: Andy Holmes <andrew g r holmes gmail com>
Date:   Sun Sep 25 14:25:25 2022 -0700

    preferences-window: plug leak in make_comparable()
    
    `pango_parse_markup()` is used to overwrite a pointer to an allocated
    string. Since the input to this function is transfer-none and the
    output is transfer-full, this leads to a leaked string.
    
    See also GNOME/gi-docgen#141 for why this probably happened.

 src/adw-preferences-window.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)
---
diff --git a/src/adw-preferences-window.c b/src/adw-preferences-window.c
index 8fbe0e2f..f192a5e0 100644
--- a/src/adw-preferences-window.c
+++ b/src/adw-preferences-window.c
@@ -138,9 +138,12 @@ make_comparable (const char        *src,
   GError *error = NULL;
 
   if (adw_preferences_row_get_use_markup (row)) {
-    pango_parse_markup (plaintext, -1, 0, NULL, &plaintext, NULL, &error);
+    char *parsed = NULL;
 
-    if (error) {
+    if (pango_parse_markup (plaintext, -1, 0, NULL, &parsed, NULL, &error)) {
+      g_free (plaintext);
+      plaintext = parsed;
+    } else {
       g_critical ("Couldn't parse markup: %s", error->message);
       g_clear_error (&error);
     }