st/nine: Prevent possible crash

In case NineBaseTexture9_ctor returns an error
This->surfaces[l] might be NULL.

Reviewed-by: Axel Davy <axel.davy@ens.fr>
Signed-off-by: Patrick Rudolph <siro@das-labor.org>

src/gallium/state_trackers/nine/texture9.c

@@ -229,7 +229,8 @@ NineTexture9_dtor( struct NineTexture9 *This )
     if (This->surfaces) {
         /* The surfaces should have 0 references and be unbound now. */
         for (l = 0; l <= This->base.base.info.last_level; ++l)
-            NineUnknown_Destroy(&This->surfaces[l]->base.base);
+            if (This->surfaces[l])
+                NineUnknown_Destroy(&This->surfaces[l]->base.base);
         FREE(This->surfaces);
     }