cmd/asm: nil deref in LOOP (PC) #12655

TEXT C(SB),$0
LOOP(PC)

panic: runtime error: invalid memory address or nil pointer dereference
[signal 0xb code=0x1 addr=0xf6 pc=0x57b0a7]

goroutine 1 [running]:
cmd/internal/obj/x86.xfol(0xc820116000, 0xc820122140, 0xc82007d7a8)
    src/cmd/internal/obj/x86/obj6.go:1174 +0x357
cmd/internal/obj/x86.follow(0xc820116000, 0xc82011e000)
    src/cmd/internal/obj/x86/obj6.go:965 +0xca
cmd/internal/obj.Writeobjdirect(0xc820116000, 0xc82000a360)
    src/cmd/internal/obj/objfile.go:295 +0x30f
main.main()
    src/cmd/asm/main.go:65 +0xd9b