xfs: only call xf{array,blob}_destroy if we have a valid pointer

In the Linux kernel, the following vulnerability has been resolved: xfs: only call xf{array,blob}_destroy if we have a valid pointer Only call the xfarray and xfblob destructor if we have a valid pointer, and be sure to null out that pointer afterwards. Note that this patch fixes a large number of commits, most of which were merged between 6.9 and 6.10.