Suggestion: add debug output for invalid script input

[NotSoRandomOne]

I was making up a script to center the screen and wasted more time than I care to admit because I didn't realize the input wasn't valid. All that happened is the entire screen went black, and zooming in/out, moving via the mouse didn't make any difference. Was able to snap out of it by searching for something/anything (the user interface (Ctrl-T) was still available).

The following is the invalid script:

test();

function test() {
   var aimT=new V3d([-0.0844507, -0.411612, 0.907438]);
   var aim=aimT.toVec3d();
   var upT =  new V3d(-0.0368663, -0.172624, 0.984298);
   var up=upT.toVec3d();
   
   StelMovementMgr.moveToJ2000(aim, up);
   }

The brackets in the first V3d constructor are invalid. Removing them fixes the problem.

After figuring that out, I was very happy! Thank you for this great tool!