Some PDF files contain JavaScript actions that consist of nothing more that one, or possibly several, empty string(s). At least to me, printing a warning/showing the fallback seems completely unnecessary in that case.
Furthermore, this patch also makes use of an early `return`, so that we no longer will attempt to check for printing instructions when no JavaScript is present in the PDF file.
*Note:* It would perhaps make sense to change the API/core code, such that we ignore empty entries there instead. However, that would probably be considered a breaking changing with respect to backwards compatibility, hence this simple viewer only solution.
Fixes 5767.