Log Message:
Update poppler* to 0.52.0.

shlib major was NOT bumped this time.

Release 0.52.0
        core:
         * Fix assert on reading some OCGs. Bug #99768
         * Properly initialize some RichMedia variables in corner cases. Bug #99767

        qt4:
         * optcontent structure was leaking the headers items. Bug #99449
         * Cleanup objects in tests to fix memory leaks. Bug #99449

        qt5:
         * optcontent structure was leaking the headers items. Bug #99449
         * Cleanup objects in tests to fix memory leaks. Bug #99449

        utils:
         * pdftocairo.1: Fix typo

Release 0.51.0
        core:
         * Check for error from NSS in SignatureHandler construct. Bug #99363
         * Add Form[Field|Widget]::setPartialName
         * Fix memory leak in PDFDoc::markAnnotations

        qt5:
         * Implement digital signature support. Bug #94378
         * Add Poppler::FormField::setName
         * Fix segfault/assert if LinkDestination is constructed with invalid \ 
input string. Bug #99357

        utils:
         * pdfunite: add fields to AcroForm dict. Bug #99141