sv.h: Correct assertion in BmUSEFUL

BmUSEFUL uses the NV slot, not the IV slot.  So asserting that it is
not IOK is not all that useful.

diff --git a/sv.h b/sv.h
index 0ba73d1..98d712d 100644 (file)
--- a/sv.h
+++ b/sv.h
@@ -1361,7 +1361,7 @@ sv_force_normal does nothing.
        (*({ SV *const _bmuseful = MUTABLE_SV(sv);                      \
            assert(SvTYPE(_bmuseful) == SVt_PVMG);                      \
            assert(SvVALID(_bmuseful));                                 \
-           assert(!SvIOK(_bmuseful));                                  \
+           assert(!SvNOK(_bmuseful));                                  \
            &(((XPVMG*) SvANY(_bmuseful))->xnv_u.xbm_useful);           \
         }))
 #else