Scene2D: handle missing texture


May happen if Qt3D hasn't created the texture yet.

Pick-to: 6.12 6.11 6.8
Change-Id: If56434a560c779ac56adaf1781b0a5007b16ab61
Reviewed-by: Paul Lemire <paul.lemire@kdab.com>
commit72a8c72d4fbb16c1f771510aaf6f22c730b0ed89
parent10da26afa50bd83b2a7b11cc5ca9345badefdab6
authorMauro Persano <mauro.persano@kdab.com>
committerMauro Persano <mauro.persano@kdab.com>
commit timeWed, 26 Aug 2026 20:13:41 +0000