crypto: make malloc failure check cross-platform

`malloc(0)` may return NULL on some platforms. Do not report
out-of-memory error unless `malloc` was passed a number greater than
`0`.

PR-URL: #8352
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Fedor Indutny <fedor@indutny.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>

src/node_crypto.cc

@@ -5368,7 +5368,7 @@ class RandomBytesRequest : public AsyncWrap {
         error_(0),
         size_(size),
         data_(static_cast<char*>(node::Malloc(size))) {
-    if (data() == nullptr)
+    if (data() == nullptr && size > 0)
       FatalError("node::RandomBytesRequest()", "Out of Memory");
     Wrap(object, this);
   }

test/parallel/parallel.status

@@ -27,11 +27,6 @@ test-debug-signal-cluster         : PASS,FLAKY
 test-fs-watch-enoent                 : FAIL, PASS
 test-fs-watch-encoding               : FAIL, PASS
 
-# being worked under https://github.com/nodejs/node/pull/7564
-test-async-wrap-post-did-throw           : PASS, FLAKY
-test-async-wrap-throw-from-callback      : PASS, FLAKY
-test-crypto-random                       : PASS, FLAKY
-
 #being worked under https://github.com/nodejs/node/issues/7973
 test-stdio-closed                        : PASS, FLAKY