Fix #98480 math when reading shared memory

shmread didn't unset SvIOK properly, causing a read into a SVIV to have
an incorrect numeric value. This patch fixes that and adds tests.

1 files changed, 2 insertions, 1 deletions

diff --git a/doio.c b/doio.c
index cb77cf67cc..1edf8d29d7 100644
--- a/doio.c
+++ b/doio.c
@@ -2278,7 +2278,8 @@ Perl_do_shmio(pTHX_ I32 optype, SV **mark, SV **sp)
 	/* suppress warning when reading into undef var (tchrist 3/Mar/00) */
 	if (! SvOK(mstr))
 	    sv_setpvs(mstr, "");
-	SvPV_force_nolen(mstr);
+	sv_upgrade(mstr, SVt_PV);
+	SvPOK_only(mstr);
 	mbuf = SvGROW(mstr, (STRLEN)msize+1);
 
 	Copy(shm + mpos, mbuf, msize, char);