Fix case where prawn-templates would cause PDF contents to disappear

[ndbroadbent]

I ran into an issue with a PDF, where prawn-templates would cause the original PDF contents to disappear after adding it's own content stream.

I figured out the reason for this - :Contents was a reference that pointed to an array of references, which is a case that prawn-templates didn't appear to handle. I've annotated a screenshot from the pdfwalker tool:

This PR just adds support for this case, which fixes the issue.

[hasmanyguitars]

@ndbroadbent Thanks for this fix! Have you seen any new issues arise from using this patch?

[ndbroadbent]

Hi @hasmanyguitars, I've been using this patch for the last few months and haven't seen any problems. It seems to work fine, but there might be a better fix, or a better way to refactor the code. I'm not too familiar with prawn-templates

[gettalong]

According to the PDF spec the /Contents key may either be a reference to a content stream or an array of references to content streams. The fix makes sure that no nested arrays are created. And there should not be any new Prawn issues due to this fix since Prawn is already aware that /Contents may be an array.

[pointlessone]

Would it be possible to split this in two distinct operations? ensure_contents_array looks a lot like a command and return value here appears to be circumstantial.

[bvogel]

This issue is VERY OLD. Is it still relevant after the latest releases?

[gettalong]

@bvogel As far as I can tell, yes, since the fix is not yet incorporated.

[petergoldstein]

@ndbroadbent I know it's been a while. Any chance you have a sample PDF around which I can build a test?

[ndbroadbent]

@petergoldstein Sorry for the delay! I'll try to create a sample PDF and add a test case that demonstrates the issue.