pdf page view prints each page on two sheets in WKWebView #1280

Found by the iOS session (opendocument-app/OpenDocument.ios#219). 7.5.2 does the same, so this is older than 7.6.0.

Repro: print a pdf page view from WKWebView (viewPrintFormatter, A4). A 38-page pdf gives 76 sheets, and every second sheet is empty.

Guess, not checked: the page box is one A4 high plus something (a margin, a border, or a rounding), so each page overflows onto a new sheet. The CSS of the page for print should be checked in WebKit: the @page size and margins, the height of .p in print, and break-after.