[perl #125541] Fix crash with %::=(); J->${\"::"}

gv_stashpvn does not expect gv_fetchpv to return something that is
not a GV.  If someone has blown away the stash with %::=(), then the
$::{"main::"} entry no longer exists, but gv_fetchpv expects it to be
there.  This patch just makes this case fail somewhat gracefully
instead of crashing:

$  ./miniperl -e '%::=(); J->${\"::"}'
Can't locate object method "" via package "" (perhaps you forgot to load ""?) at -e line 1.

If someone does %::=(), nothing more reasonable should be expected.
At least it does not crash now.

1 files changed, 1 insertions, 1 deletions

diff --git a/gv.c b/gv.c
index 821a3834b8..651a7aa76f 100644
--- a/gv.c
+++ b/gv.c
@@ -1411,7 +1411,7 @@ S_gv_stashpvn_internal(pTHX_ const char *name, U32 namelen, I32 flags)
     tmpgv = gv_fetchpvn_flags(tmpbuf, tmplen, flags, SVt_PVHV);
     if (tmpbuf != smallbuf)
 	Safefree(tmpbuf);
-    if (!tmpgv)
+    if (!tmpgv || !isGV_with_GP(tmpgv))
 	return NULL;
     stash = GvHV(tmpgv);
     if (!(flags & ~GV_NOADD_MASK) && !stash) return NULL;