Fall back to sector after bootloader if no partition table is found

x86_64/partitions.asm

@@ -29,8 +29,6 @@ find_redoxfs_partition:
 .notfound:
     mov si, .no_partition_found_msg
     call print
-.halt:
-    cli
-    hlt
-    jmp .halt
+    mov eax, (startup_end - boot) / 512
+    ret
 .no_partition_found_msg: db "No MBR partition with type 0x83 found", 0xA, 0xD, 0