fix chomping newline only line

* string.c (chomp_newline): fix chomping newline only line.
  rb_enc_prev_char return NULL if no previous character and must
  not call rb_enc_ascget on it.  a patch by Ary Borenszweig
  <asterite AT gmail.com> at [ruby-core:78666].  [Bug #13037]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@57088 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

1 files changed, 1 insertions, 1 deletions

diff --git a/string.c b/string.c
index 8515773a84..fd17355346 100644
--- a/string.c
+++ b/string.c
@@ -7409,7 +7409,7 @@ chomp_newline(const char *p, const char *e, rb_encoding *enc)
     if (rb_enc_is_newline(prev, e, enc)) {
 	e = prev;
 	prev = rb_enc_prev_char(p, e, e, enc);
-	if (rb_enc_ascget(prev, e, NULL, enc) == '\r')
+	if (prev && rb_enc_ascget(prev, e, NULL, enc) == '\r')
 	    e = prev;
     }
     return e;