pdfrenderer.cpp: Ignore non-text blocks

[amitdo]

Fix #3957.

[amitdo]

@egorpugin,

Can you fix sw?

[egorpugin]

I'll check sw issues.

[amitdo]

Here is the pdf file that Tesseract produces after applying the patch from this PR.

3957.pdf

[amitdo]

Here is the pdf file that Tesseract produces before applying the patch from this PR.

3957-0.pdf

[amitdo]

Doing 'select all', 'copy' and then 'paste' to a text file, and using pdftotxt as another method for testing. There is no spaces, for both 'before' and 'after' PDFs.

Still, there is a difference internally between the files. The 'after' pdf is slightly smaller (in bytes) than the 'before' pdf file.

[amitdo]

Waiting for a feedback from @bleze.

[amitdo]

https://www.pdf-online.com/osa/validate.aspx

File 3957-0.pdf
Compliance pdf1.5
Result Document validated successfully.
Details

Validating file "3957-0.pdf" for conformance level pdf1.5

The document does conform to the PDF 1.5 standard.

File 3957.pdf
Compliance pdf1.5
Result Document validated successfully.
Details

Validating file "3957.pdf" for conformance level pdf1.5

The document does conform to the PDF 1.5 standard.

[amitdo]

@stweil, can I merge this PR?

It removes unneeded stuff from the pdf output in documents with non-text blocks and make the document slightly smaller in bytes.

[stweil]

Looks good, thank you!

[bleze]

Waiting for a feedback from @bleze.

I already took the code from the patch and applied to my copy. I can confirm that the spaces are no longer included in the output. Thank you for fixing this!