uboot-imx

gadget: f_thor: check pointers before use in download_tail()

Some pointers in function download_tail() were not checked
before the use. This could possibly cause the data abort.
To avoid this, check if the pointers are not null is added.

Signed-off-by: Przemyslaw Marczak <p.marczak@samsung.com>
Tested-by: Lukasz Majewski <l.majewski@samsung.com>
[TestHW: Exynos4412-Trats2]