Removed empty src attribute from img tag. Fixes #276

[MazeChaZer]

The empty src attribute triggers strange behavior in IE 8 and is a bad practice in general.
If lightbox is used on http://example.com/product/123 IE 8 makes a request to http://example.com/product/ to fetch the image. This caused Exceptions invisible in the browser that we needed half a day to track down.
Chrome and Safari (at least in older versions) try to load the image from http://example.com/product/123, so this can double the traffic on your website in the worst case.
See also http://www.nczonline.net/blog/2009/11/30/empty-image-src-can-destroy-your-site/

[the-real-tokai]

An "img" tag without "src" is not valid, see: http://dev.w3.org/html5/spec-preview/the-img-element.html

"The src attribute must be present, and must contain a valid non-empty URL potentially surrounded by spaces referencing a non-interactive, optionally animated, image resource that is neither paged nor scripted."

I did a similar patch (see pull request #280) which adds a dummy "data:" url to the empty src to fix the issues in the browsers. This is not ideal either though. IMHO the whole tag should first be injected to the html when it is actually needed. I guess that requires a slightly more elaborate patch than our both solutions. ;)

[rulin132]

maybe instead of removing the src tag, which may fix one issue, but introduce other issues, might be better to use the old blank gif trick. a base64 1x1 gif will probably be the best solution if no valid src URL has been provided.

[MazeChaZer]

I agree. Closing this pull request in favor of #280.