tdf#95220: Check if DrawingLayer is not nullptr

bool ScDocShell::isTiledRendering() const crashed without this check

Change-Id: Idb7ace05eb1aa37cbc3d956503c046b0e9b9d0e5
Reviewed-on: https://gerrit.libreoffice.org/19570Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Eike Rathke <erack@redhat.com>
Tested-by: Eike Rathke <erack@redhat.com>

sc/source/ui/docshell/docsh.cxx

@@ -3196,7 +3196,7 @@ void ScDocShell::libreOfficeKitCallback(int nType, const char* pPayload) const
 
 bool ScDocShell::isTiledRendering() const
 {
-    return aDocument.GetDrawLayer()->isTiledRendering();
+    return aDocument.GetDrawLayer() && aDocument.GetDrawLayer()->isTiledRendering();
 }
 
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