Btrfs: check for NULL pointer in updating reloc roots
Btrfs: check for NULL pointer in updating reloc roots

Add a check for NULL pointer to avoid invalid reference.

Signed-off-by: Liu Bo <53bcb7ec3fc64af6813d2ef7ceefe23b63265886@oracle.com>
Signed-off-by: Josef Bacik <631dfb3d07694fdcf26abc7aac2c6c2b641f8bde@fusionio.com>

KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas,KristFoundation/Programs,KristFoundation/Programs,TeamVee-Kanas/android_kernel_samsung_kanas