Check whether gX86PagingMethod is NULL in arch_vm_translation_map_is_kernel_page_accessible.

This means that the kernel debugger won't cause a recursive panic if a
panic occurs before vm_init().

src/system/kernel/arch/x86/arch_vm_translation_map.cpp

@@ -144,5 +144,8 @@ bool
 arch_vm_translation_map_is_kernel_page_accessible(addr_t virtualAddress,
 	uint32 protection)
 {
+	if (!gX86PagingMethod)
+		return true;
+
 	return gX86PagingMethod->IsKernelPageAccessible(virtualAddress, protection);
 }