dump.c: Don’t dump CvOUTSIDE SV when there is none

$ ./perl -Ilib -MDevel::Peek -Mfeature=:all -Xle 'my sub f; Dump \&f'
SV = IV(0x7fd7138312b0) at 0x7fd7138312c0
  REFCNT = 1
  FLAGS = (TEMP,ROK)
  RV = 0x7fd713831b90
  SV = PVCV(0x7fd7138303d0) at 0x7fd713831b90
    REFCNT = 2
    FLAGS = (CLONED,DYNFILE,NAMED,LEXICAL)
    COMP_STASH = 0x7fd713807ce8	"main"
    ROOT = 0x0
    NAME = "f"
    FILE = "-e"
    DEPTH = 0
    FLAGS = 0x19040
    OUTSIDE_SEQ = 187
    PADLIST = 0x7fd7134067e8
    PADNAME = 0x7fd713411f88(0x7fd713406d48) PAD = 0x7fd713807e68(0x7fd71340d2f8)
    OUTSIDE = 0x0 (null)
    SV = 0

That final ‘SV = 0’ is very confusing!