In amagic_call(), offset should be strictly lesser than the SV len to…

… be allowed to access the corresponding string buffer byte

gv.c

@@ -1869,7 +1869,7 @@ Perl_amagic_call(pTHX_ SV *left, SV *right, int method, int flags)
 	  char *pv = SvPV(lex_mask, len);
 
 	  /* Bit set, so this overloading operator is disabled */
-	  if ( (STRLEN)offset <= len && pv[offset] & ( 1 << bit ) )
+	  if ( (STRLEN)offset < len && pv[offset] & ( 1 << bit ) )
 	      return NULL;
       }
   }