Fix WikiPage.from_param

app/controllers/wiki_controller.rb

@@ -164,7 +164,7 @@ class WikiController < ApplicationController
     @course = Course.from_param(params[:course_id])
 
     if params[:id]
-      @wiki_page = WikiPage.from_param(params[:id])
+      @wiki_page = WikiPage.from_param(@course, params[:id])
     else
       @wiki_page = WikiPage.new(params[:wiki_page])
     end

app/models/course.rb

@@ -88,6 +88,6 @@ class Course < ActiveRecord::Base
   end
 
   def self.from_param(param)
-    param.is_numeric? ? Course.find(param) : Course.find_by_short_name(param)
+    param.is_numeric? ? Course.find(param) : Course.find_by_short_name!(param)
   end
 end

app/models/wiki_page.rb

@@ -79,11 +79,11 @@ class WikiPage < ActiveRecord::Base
     canonical_title || id
   end
 
-  def self.from_param(param)
+  def self.from_param(course, param)
     if param.is_numeric?
-      WikiPage.find!(param)
+      course.wiki_pages.find(param)
     else
-      WikiPage.find_by_canonical_title!(param)
+      course.wiki_pages.find_by_canonical_title!(param)
     end
   end