added logic to abort applying the scPlayer() if the source element has already had an scPlayer assigned

I found through some dodgy JS code of my own that multiple calls of `scPlayer()` on a source element weren't being aborted if the `scPlayer()` functionality was already applied. This resulted in the internal links of the generated `scPlayer()` element (such as `#play`, `#pause`, `#info`, etc.) to then try to be referenced as `scApiUrl()`s which then resulted in errors and no media being loaded.

I think ideally all the var setting logic which involves DOM-crawling would follow the abort code so as to lower any further unnecessary overheads.