Non explicit error message when setting active a Viewport that is already active

[Flarkk]

Godot version

4.0 dev, 3.x

System information

All

Issue description

When calling VisualServer::viewport_set_active(viewport, true) on a Viewport that is already active, the engine prints the following non explicit error message (tested with Godot 3.1.2, but true on all 3.x and 4.0-dev) :

E 0:00:05:0437   Condition ' active_viewports.find(viewport) != -1 ' is true.
  <C Source>     servers/visual/visual_server_viewport.cpp:369 @ viewport_set_active()

This message is triggered as following (see actual code) :
ERR_FAIL_COND(active_viewports.find(viewport) != -1); //already active

The message should be more explicit, for instance Can't make active a Viewport that is already active.
By the way I'm wondering if any error is supposed to be raised at all here (should be preferable not to fail and do nothing silently ?)

Steps to reproduce

Make active any Viewport that is already active.

Minimal reproduction project

No response