Don't show next/previous page options if only one page

It's possible to get one page of levels by removing all the built-ins,
either by removing them directly from data.zip or by putting files with
the same filenames as them in your level folder that don't contain
nothing.

And hey, there's already a check for if no levels exist at all, so why
not check for this too?

desktop_version/src/Game.cpp

@@ -6002,21 +6002,24 @@ void Game::createmenu( enum Menu::MenuName t, bool samemenu/*= false*/ )
                     option(text);
                 }
             }
-            if((size_t) ((levelpage*8)+8) <ed.ListOfMetaData.size())
+            if (ed.ListOfMetaData.size() > 8)
             {
-                option("next page");
-            }
-            else
-            {
-                option("first page");
-            }
-            if (levelpage == 0)
-            {
-                option("last page");
-            }
-            else
-            {
-                option("previous page");
+                if((size_t) ((levelpage*8)+8) <ed.ListOfMetaData.size())
+                {
+                    option("next page");
+                }
+                else
+                {
+                    option("first page");
+                }
+                if (levelpage == 0)
+                {
+                    option("last page");
+                }
+                else
+                {
+                    option("previous page");
+                }
             }
             option("return to menu");