Added ltrim to $url in fetch_file_contents()...

...to fix cases where a URL has one or more spaces before it.

This is a pretty edge case, but there's one feed I found in which the site stupidly adds a space before image tags' `src` URLs. Because fetch_file_contents() replaces spaces with %20 (for encoding reasons) the URL becomes `%20https://` which causes CURL to gracefully fail with an invalid protocol error. This patch left trims any space characters that precede the URL, while leaving the remaining spaces to be encoded.