cleanup two column panning

It's important for us to take maring into account because rouding error
can force us to skip right marging. However, this shouldn't be done
when not in pan_by_page mode, so this diff is artifically large

unireader.lua

@@ -581,31 +581,32 @@ function UniReader:inputloop()
 				local old_offset_y = self.offset_y
 
 				if ev.code == KEY_FW_LEFT then
+					print("# KEY_FW_LEFT "..self.offset_x.." + "..x.." > 0");
 					self.offset_x = self.offset_x + x
-					if self.offset_x > 0 then
-						self.offset_x = 0
-						if self.pan_by_page and self.pageno > 1 then
+					if self.pan_by_page then
+						if self.offset_x > 0 and self.pageno > 1 then
 							self.offset_x = self.pan_x
 							self.offset_y = self.min_offset_y -- bottom
 							self:goto(self.pageno - 1)
+						else
+							self.offset_y = self.min_offset_y
 						end
-					end
-					if self.pan_by_page then
-						self.offset_y = self.min_offset_y
+					elseif self.offset_x > 0 then
+						self.offset_x = 0
 					end
 				elseif ev.code == KEY_FW_RIGHT then
-					print("# FW RIGHT "..self.offset_x.." - "..x.." < "..self.min_offset_x);
+					print("# KEY_FW_RIGHT "..self.offset_x.." - "..x.." < "..self.min_offset_x);
 					self.offset_x = self.offset_x - x
-					if self.offset_x < self.min_offset_x then
-						self.offset_x = self.min_offset_x
-						if self.pan_by_page and self.pageno < self.doc:getPages() then
+					if self.pan_by_page then
+						if self.offset_x < self.min_offset_x - self.pan_margin and self.pageno < self.doc:getPages() then
 							self.offset_x = self.pan_x
 							self.offset_y = self.pan_y
 							self:goto(self.pageno + 1)
+						else
+							self.offset_y = self.pan_y
 						end
-					end
-					if self.pan_by_page then
-						self.offset_y = self.pan_y
+					elseif self.offset_x < self.min_offset_x then
+						self.offset_x = self.min_offset_x
 					end
 				elseif ev.code == KEY_FW_UP then
 					self.offset_y = self.offset_y + y