player: osd: fix memory leak on vlc_memstream

Fix memstream stream being open but never closed when zero tracks were
to be displayed to the OSD. The code was opening the vlc_memstream from
the start but was freeing the pointer only when the close of the
memstream succeeded AND the number of tracks was non-null.

Instead, this patch reorder the code so that the vlc_memstream is
allocated only when there is at least one track to display and early
exit with the N/A OSD message otherwise.

Then it tries to close the memstream and exit in case of error.

Finally, the text is sent to the OSD and the pointer is freed.

It was raising an ASAN leak report on test_src_player through the
test_teletext test function.

Fixes #26732

src/player/osd.c

@@ -210,7 +210,6 @@ vlc_player_osd_Tracks(vlc_player_t *player, vlc_es_id_t * const *selected, vlc_e
     const char *cat_name = es_format_category_to_string(cat);
     int tracks_count = 0;
     struct vlc_memstream stream;
-    vlc_memstream_open(&stream);
 
     for (size_t i = 0; selected[i] != NULL; i++)
     {
@@ -225,23 +224,37 @@ vlc_player_osd_Tracks(vlc_player_t *player, vlc_es_id_t * const *selected, vlc_e
         if (unlikely(track == NULL))
             continue;
 
-        if (tracks_count != 0)
+        /* Open the stream for the first track, and exit in case of error.
+         * On the next tracks, add comma to separate the track names. */
+        if (tracks_count == 0)
+        {
+            if (vlc_memstream_open(&stream) != 0)
+                return;
+        }
+        else
             vlc_memstream_puts(&stream, ", ");
+
         vlc_memstream_puts(&stream, track->name);
         tracks_count++;
     }
 
-    if (vlc_memstream_close(&stream) == 0 && tracks_count != 0)
+    if (tracks_count == 0)
     {
-        if (tracks_count == 1)
-            vlc_player_osd_Message(player, _("%s track: %s"), cat_name,
-                                   stream.ptr);
-        else
-            vlc_player_osd_Message(player, _("%s tracks: %s"), cat_name,
-                                   stream.ptr);
-        free(stream.ptr);
-    } else if (tracks_count == 0)
         vlc_player_osd_Message(player, _("%s track: %s"), cat_name, _("N/A"));
+        return;
+    }
+
+    /* The vlc_memstream is opened only if tracks_count != 0. */
+    if (vlc_memstream_close(&stream) != 0)
+        return;
+
+    if (tracks_count == 1)
+        vlc_player_osd_Message(player, _("%s track: %s"), cat_name,
+                               stream.ptr);
+    else
+        vlc_player_osd_Message(player, _("%s tracks: %s"), cat_name,
+                               stream.ptr);
+    free(stream.ptr);
 }
 
 void