crypto: don't assert when calling Cipher#final() twice

Remove the assert() that triggered when Cipher#final() or
Decipher#final() was called twice.

Fixes #4886.

src/node_crypto.cc

@@ -2301,11 +2301,7 @@ class Cipher : public ObjectWrap {
 
     int r = cipher->CipherFinal(&out_value, &out_len);
 
-    assert(out_value != NULL);
-    assert(out_len != -1 || r == 0);
-
-    if (out_len == 0 || r == 0) {
-      // out_value always get allocated.
+    if (out_len <= 0 || r == 0) {
       delete[] out_value;
       if (r == 0) {
         Local<Value> exception = Exception::TypeError(
@@ -2756,10 +2752,7 @@ class Decipher : public ObjectWrap {
 
     int r = cipher->DecipherFinal<TOLERATE_PADDING>(&out_value, &out_len);
 
-    assert(out_value != NULL);
-    assert(out_len != -1);
-
-    if (out_len == 0 || r == 0) {
+    if (out_len <= 0 || r == 0) {
       delete [] out_value; // allocated even if out_len == 0
       if (r == 0) {
         Local<Value> exception = Exception::TypeError(

test/simple/test-crypto.js

@@ -665,3 +665,16 @@ crypto.pbkdf2('pass\0word', 'sa\0lt', 4096, 16, function(err, result) {
 assert.throws(function() {
   crypto.pbkdf2('password', 'salt', 1, 20, null);
 });
+
+// Calling Cipher.final() or Decipher.final() twice should error but
+// not assert. See #4886.
+(function() {
+  var c = crypto.createCipher('aes-256-cbc', 'secret');
+  try { c.final('xxx') } catch (e) { /* Ignore. */ }
+  try { c.final('xxx') } catch (e) { /* Ignore. */ }
+  try { c.final('xxx') } catch (e) { /* Ignore. */ }
+  var d = crypto.createDecipher('aes-256-cbc', 'secret');
+  try { d.final('xxx') } catch (e) { /* Ignore. */ }
+  try { d.final('xxx') } catch (e) { /* Ignore. */ }
+  try { d.final('xxx') } catch (e) { /* Ignore. */ }
+})();