Fixes crash in timer.

[bjaekel]

FIxes error in setTimer and setInterval call in JavaScript. An example for the crash can be:

consolo.log('setting up a timer'); let timeoutId; timeoutId = setTimeout(function() { consolo.log('timeout executed, but calling clearTimeout()'); clearTimeout(timeoutId); consolo.log('after timeout executed.'); }, 1000);

consolo.log('setting up a timer'); let timeoutId; timeoutId = setInterval(function() { consolo.log('timeout executed, but calling clearTimeout()'); clearTimeout(timeoutId); consolo.log('after timeout executed.'); }, 1000);

Usefull information:

• https://github.com/libuv/libuv/blob/v1.x/include/uv.h
• https://github.com/nodejs/node/blob/master/deps/uv/src/unix/core.c (uv__run_closing_handles ends up in an infinity loop if crash is only fixed by null pointer check)