qr: print_oops: don't try to print if there is no framebuffer

If the kernel boots in textmode, we would hit a null pointer derefernce
in compute_w(). Prevent this by actually checking the value of info.

Signed-off-by: Levente Kurusa <levex@linux.com>
Merge pull request #2 from levex/for-teodora

Fix a null pointer dereference