Kernel: Make validate_read_from_kernel() return early for nullptr checks.

Null pointers are always invalid, so don't bother going through all the
various checks for them.

Kernel/Process.cpp

@@ -1371,6 +1371,8 @@ static KernelMemoryCheckResult check_kernel_memory_access(LinearAddress laddr, b
 
 bool Process::validate_read_from_kernel(LinearAddress laddr) const
 {
+    if (laddr.is_null())
+        return false;
     // We check extra carefully here since the first 4MB of the address space is identity-mapped.
     // This code allows access outside of the known used address ranges to get caught.
     auto kmc_result = check_kernel_memory_access(laddr, false);