Fix for [perl #52074] Segfault on ISA push after symbol table delete

This restores the 5.8.8 behaviour. The deleted stash is not vivified
again, hence the hierarchy remains broken. But there's no segfault.

p4raw-id: //depot/perl@33684

1 files changed, 4 insertions, 2 deletions

diff --git a/mg.c b/mg.c
index 0bc79798f1..dfe1fb7d80 100644
--- a/mg.c
+++ b/mg.c
@@ -1607,7 +1607,8 @@ Perl_magic_setisa(pTHX_ SV *sv, MAGIC *mg)
             : (GV*)SvMAGIC(mg->mg_obj)->mg_obj
     );
 
-    mro_isa_changed_in(stash);
+    if (stash)
+	mro_isa_changed_in(stash);
 
     return 0;
 }
@@ -1632,7 +1633,8 @@ Perl_magic_clearisa(pTHX_ SV *sv, MAGIC *mg)
             : (GV*)SvMAGIC(mg->mg_obj)->mg_obj
     );
 
-    mro_isa_changed_in(stash);
+    if (stash)
+	mro_isa_changed_in(stash);
 
     return 0;
 }