luaA_window_get_opacity: Always return a number

What's the point of distinguishing between "opacity 1" and "no opacity set"?
This commit makes awesome handle both cases identically.

Signed-off-by: Uli Schlachter <psychon@znc.in>

objects/window.c

@@ -131,12 +131,12 @@ static int
 luaA_window_get_opacity(lua_State *L, window_t *window)
 {
     if(window->opacity >= 0)
-    {
         lua_pushnumber(L, window->opacity);
+    else
+        /* Let's always return some "good" value */
+        lua_pushnumber(L, 1);
     return 1;
 }
-    return 0;
-}
 
 /** Set the window border color.
  * \param L The Lua VM state.