Fix SDL_GL_ACCELERATED_VISUAL on Windows in the 1.3 branch.

Fixes Bugzilla #1254.

Thanks to Thilo Schulz for the patch!

src/video/windows/SDL_windowsopengl.c

@@ -466,9 +466,11 @@ WIN_GL_SetupWindow(_THIS, SDL_Window * window)
         *iAttr++ = _this->gl_config.multisamplesamples;
     }
 
-    *iAttr++ = WGL_ACCELERATION_ARB;
-    *iAttr++ = (_this->gl_config.accelerated ? WGL_FULL_ACCELERATION_ARB :
-                                               WGL_NO_ACCELERATION_ARB);
+    if ( this->gl_config.accelerated >= 0 ) {
+        *iAttr++ = WGL_ACCELERATION_ARB;
+        *iAttr++ = (_this->gl_config.accelerated ? WGL_FULL_ACCELERATION_ARB :
+                                                   WGL_NO_ACCELERATION_ARB);
+    }
 
     *iAttr = 0;