add preLoadSettings methods for cache_document_size setting

cache_document_size should be configurable for
every docuemnt and it must be loaded before
document open, so I added the preLoadSettings method

reader.lua

@@ -49,6 +49,7 @@ function openFile(filename)
 	end
 	if reader then
 		InfoMessage:show("Opening document, please wait... ", 0)
+		reader:preLoadSettings(filename)
 		local ok, err = reader:open(filename)
 		if ok then
 			reader:loadSettings(filename)

unireader.lua

@@ -907,11 +907,19 @@ function UniReader:initGlobalSettings(settings)
 	end
 end
 
+-- Method to load settings before document open
+function UniReader:preLoadSettings(filename)
+	self.settings = DocSettings:open(filename)
+
+	local cache_d_size = self.settings:readSetting("cache_document_size")
+	if cache_d_size then
+		self.cache_document_size = cache_d_size
+	end
+end
+
 -- This is a low-level method that can be shared with all readers.
 function UniReader:loadSettings(filename)
 	if self.doc ~= nil then
-		self.settings = DocSettings:open(filename,self.cache_document_size)
-
 		local gamma = self.settings:readSetting("gamma")
 		if gamma then
 			self.globalgamma = gamma