Fix OCR fails on native djvu pages

The page_width and page_height were always 600 and 800 before this patch
rendering the OCR engine confused.

This should fix #1379.

base

@@ -1 +1 @@
-Subproject commit 57d4cca62d6e1f14c32bf883a4d3b3ff63b2a9cd
+Subproject commit 5af9c0e97716d94df47ad07a3639263a6ed49e3d

frontend/document/koptinterface.lua

@@ -620,7 +620,9 @@ function KoptInterface:getNativeOCRWord(doc, pageno, rect)
         kc:setZoom(30/rect.h)
         local page = doc._document:openPage(pageno)
         page:getPagePix(kc)
+        --kc:exportSrcPNGFile({rect}, nil, "ocr-word.png")
         local word_w, word_h = kc:getPageDim()
+        --DEBUG(word_w, word_h)
         local ok, word = pcall(
             kc.getTOCRWord, kc, "src",
             0, 0, word_w, word_h,