[njs] String.prototype.repeat method fix.

[Andrey Zelenkov]

details:   http://hg.nginx.org/njs/rev/ff8f717db1be
branches:  
changeset: 234:ff8f717db1be
user:      Andrey Zelenkov <zelenkov at nginx.com>
date:      Thu Nov 03 18:12:10 2016 +0300
description:
String.prototype.repeat method fix.

Found with afl-fuzz.

diffstat:

 njs/njs_string.c         |  5 +++++
 njs/test/njs_unit_test.c |  3 +++
 2 files changed, 8 insertions(+), 0 deletions(-)

diffs (28 lines):

diff -r d7a10c0dfcce -r ff8f717db1be njs/njs_string.c
--- a/njs/njs_string.c	Mon Oct 31 16:28:12 2016 +0300
+++ b/njs/njs_string.c	Thu Nov 03 18:12:10 2016 +0300
@@ -1756,6 +1756,11 @@ njs_string_prototype_repeat(njs_vm_t *vm
 
     (void) njs_string_prop(&string, &args[0]);
 
+    if (string.size == 0) {
+        vm->retval = njs_string_empty;
+        return NXT_OK;
+    }
+
     if (nargs > 1) {
         max = NJS_STRING_MAX_LENGTH / string.size;
         n = args[1].data.u.number;
diff -r d7a10c0dfcce -r ff8f717db1be njs/test/njs_unit_test.c
--- a/njs/test/njs_unit_test.c	Mon Oct 31 16:28:12 2016 +0300
+++ b/njs/test/njs_unit_test.c	Thu Nov 03 18:12:10 2016 +0300
@@ -3618,6 +3618,9 @@ static njs_unit_test_t  njs_test[] =
     { nxt_string("'абв'.repeat(3)"),
       nxt_string("абвабвабв") },
 
+    { nxt_string("''.repeat(3)"),
+      nxt_string("") },
+
     { nxt_string("'abc'.repeat(0)"),
       nxt_string("") },