Pool size and promise-rejections

[czaefferer]

If the poolLimit is bigger than the input array, an "UnhandledPromiseRejectionWarning" is caused for every rejection. Take for example this code:

const asyncPool = require('tiny-async-pool');
const handler = async () => {
  const poolLimit = 2;
  const timeout = i => new Promise((resolve, reject) => setTimeout(() => reject(i), i));
  await asyncPool(poolLimit, [100, 500, 300, 200], timeout).catch(error => {console.log(error);});
};
handler();

Every promise is rejected, so the pool stops and rejects after the very first rejection, and the output is:

100

This is working as expected, but once I increase the poolLimit to 5 (or more, as long as it's bigger than the number of elements in the input array), the output looks like this:

100
(node:6106) UnhandledPromiseRejectionWarning: 100
(node:6106) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 1)
(node:6106) [DEP0018] DeprecationWarning: Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
(node:6106) UnhandledPromiseRejectionWarning: 200
(node:6106) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 2)
(node:6106) UnhandledPromiseRejectionWarning: 300
(node:6106) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 3)
(node:6106) UnhandledPromiseRejectionWarning: 500
(node:6106) UnhandledPromiseRejectionWarning: Unhandled promise rejection. This error originated either by throwing inside of an async function without a catch block, or by rejecting a promise which was not handled with .catch(). (rejection id: 4)

[rxaviers]

Thanks for filing this issue! I'd be happy to accept a PR with a fix.