Slow loading if no images found.

[lcdsantos]

When the page has no images, the plugin wait for the maxTime to complete, instead of just completing right away.

Example:
http://jsbin.com/dureti/edit?html,output - Contains 1 image, loads pretty fast.
http://jsbin.com/henaba/edit?html,output - Has no images, takes really long time to complete.

What if we add a check after getImageSrcs function on

queryloader2/src/ImagePreloader/index.js

Line 29 in 183e0c0

this.sources = this.getImageSrcs(element);

if (this.sources.length === 0) {
  this.done === true;
  this.updateProgress();
}

[Gaya]

Sounds like a good plan!
You can add a pull request if you'd like to fix this problem.