Fix "No loader found for resource ... .svg.import"

[hsandt]

Only load actual .svg, not their .import files

Repro:
In the editor, run game and open the Visual Debugger panel. You will see many errors like:

E 0:00:00.315 _load: No loader found for resource: res://VisualDebugger/icons/icon_a_r_v_r_anchor.svg.import.
<C++ Error> Method failed. Returning: RES()
<C++ Source> core/io/resource_loader.cpp:285 @ _load()
Outliner.gd:32 @ load_textures()
Outliner.gd:36 @ _ready()
VDGlobal.gd:24 @ _ready()