Fix assertion failure with -DT -e\"

$ ./perl -DT -e\"
Assertion failed: (s), function S_printbuf, file toke.c, line 479.
Abort trap: 6

1 files changed, 7 insertions, 1 deletions

diff --git a/toke.c b/toke.c
index 54403b0812..e738311d46 100644
--- a/toke.c
+++ b/toke.c
@@ -6835,7 +6835,13 @@ Perl_yylex(pTHX)
 
     case '"':
 	s = scan_str(s,!!PL_madskills,FALSE,FALSE, FALSE);
-	DEBUG_T( { printbuf("### Saw string before %s\n", s); } );
+	DEBUG_T( {
+	    if (s)
+		printbuf("### Saw string before %s\n", s);
+	    else
+		PerlIO_printf(Perl_debug_log,
+			     "### Saw unterminated string\n");
+	} );
 	if (PL_expect == XOPERATOR) {
 	    if (PL_lex_formbrack && PL_lex_brackets == PL_lex_formbrack) {
 		return deprecate_commaless_var_list();