Make link to PDF page that does not exist unselectable.

Uses the new FPDFDest_GetDestPageIndex call in PDFium.

Bug: pdfium:938
Change-Id: I6e35cb5c8b257bd3d07fd0d05a8260a7fb6681e1
Reviewed-on: https://chromium-review.googlesource.com/894148
Commit-Queue: Henrique Nakashima <hnakashima@chromium.org>
Reviewed-by: dsinclair <dsinclair@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#533785}

pdf/pdfium/pdfium_page.cc

@@ -360,14 +360,17 @@ PDFiumPage::Area PDFiumPage::GetDestinationTarget(FPDF_DEST destination,
   if (!target)
     return NONSELECTABLE_AREA;
 
-  target->page = FPDFDest_GetPageIndex(engine_->doc(), destination);
+  int page_index = FPDFDest_GetDestPageIndex(engine_->doc(), destination);
+  if (page_index < 0)
+    return NONSELECTABLE_AREA;
+
+  target->page = page_index;
 
   base::Optional<std::pair<float, float>> xy = GetPageXYTarget(destination);
   if (!xy)
     return DOCLINK_AREA;
 
   target->y_in_pixels = TransformPageToScreenXY(xy.value()).second;
-
   return DOCLINK_AREA;
 }