drm/i915: Fix NULL ptr deref by checking new_crtc_state

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: drm/i915: Fix NULL ptr deref by checking new_crtc_state intel_atomic_get_new_crtc_state can return NULL, unless crtc state wasn't obtained previously with intel_atomic_get_crtc_state, so we must check it for NULLness here, just as in many other places, where we can't guarantee that intel_atomic_get_crtc_state was called. We are currently getting NULL ptr deref because of that, so this fix was confirmed to help. (cherry picked from commit 1d5b09f8daf859247a1ea65b0d732a24d88980d8)

References

• https://git.kernel.org/stable/c/dbf25cc21beff4fd2e730573845a266504b21bb2
• https://git.kernel.org/stable/c/8b3c0d2d1685ba40b0af4ee1f8d8824a73870f88
• https://git.kernel.org/stable/c/a41d985902c153c31c616fe183cf2ee331e95ecb