Fix footnotes and markers with full status bar

Take full/top status bar's height into account when
computing coordinates.
Also wrap getPageMargins() in CreDocument, so we
don't use cre.cpp _document directly anywhere else.

frontend/apps/reader/modules/readerlink.lua

@@ -257,11 +257,15 @@ end
 --- Check if a xpointer to <a> node really points to itself
 function ReaderLink:isXpointerCoherent(a_xpointer)
     -- Get screen coordinates of xpointer
-    local doc_margins = self.ui.document._document:getPageMargins()
+    local doc_margins = self.ui.document:getPageMargins()
+    local header_height = self.ui.document:getHeaderHeight() -- top full status bar (0 when bottom mini bar used)
     local doc_y, doc_x = self.ui.document:getPosFromXPointer(a_xpointer)
     local top_y = self.ui.document:getCurrentPos()
     -- (strange, but using doc_margins.top is accurate even in scroll mode)
-    local screen_y = doc_y - top_y + doc_margins["top"]
+    local screen_y = doc_y - top_y
+    if self.view.view_mode == "page" then
+        screen_y = screen_y + doc_margins["top"] + header_height
+    end
     local screen_x = doc_x + doc_margins["left"]
     -- Get again link and a_xpointer from this position
     local re_link_xpointer, re_a_xpointer = self.ui.document:getLinkFromPosition({x = screen_x, y = screen_y}) -- luacheck: no unused
@@ -1045,7 +1049,7 @@ function ReaderLink:showAsFootnotePopup(link, neglect_current_location)
     popup = FootnoteWidget:new{
         html = html,
         doc_font_size = Screen:scaleBySize(self.ui.font.font_size),
-        doc_margins = self.ui.document._document:getPageMargins(),
+        doc_margins = self.ui.document:getPageMargins(),
         close_callback = close_callback,
         follow_callback = function() -- follow the link on swipe west
             UIManager:close(popup)