Fix rare bugs identified by fuzzing

frontend/ui/reader/readerdictionary.lua

@@ -34,7 +34,7 @@ function ReaderDictionary:stardictLookup(word, box)
 end
 
 function ReaderDictionary:showDict(results, box)
-	if results and results[1] then
+	if results and results[1] and box then
 		DEBUG("showing quick lookup dictionary window")
 		local align = nil
 		local region = Geom:new{x = 0, w = Screen:getWidth()}

frontend/ui/reader/readerfooter.lua

@@ -77,6 +77,7 @@ function ReaderFooter:init()
 end
 
 function ReaderFooter:updateFooter()
+	if type(self.pageno) ~= "number" then return end
 	self.progress_bar.percentage = self.pageno / self.pages
 	if self.show_time then
 		self.progress_text.text = os.date("%H:%M")

frontend/ui/reader/readerlink.lua

@@ -53,9 +53,11 @@ end
 function ReaderLink:onTap(arg, ges)
 	if self.ui.document.info.has_pages then
 		local pos = self.view:screenToPageTransform(ges.pos)
-		local link = self.ui.document:getLinkFromPosition(pos.page, pos)
-		if link then
-			return self:onGotoLink(link)
+		if pos then
+			local link = self.ui.document:getLinkFromPosition(pos.page, pos)
+			if link then
+				return self:onGotoLink(link)
+			end
 		end
 	else
 		local link = self.ui.document:getLinkFromPosition(ges.pos)