Infinite loop freezes up browser; doesn't display loop protector error

Reported in ZenDesk.

Students code locks up browser (Chrome) instead of showing infinite loop error.

The code was:

```
background(219, 255, 255);

//roof
fill(174, 180, 214);
triangle(200, 28, 350, 150, 50, 150);
//actual house
fill(209, 181, 157);
rect(60, 150, 280, 207);
//door
fill(120, 80, 19);
rect(180, 280, 40, 77);
//window
fill(255, 255, 255);

for (var i = 90; i < 400; i+20){
var x = 90;
rect(x, 190, 50, 70);
x += 100;
}

//grass and short trees
var x = 0;
var grass = getImage("cute/GrassBlock");
var tree = getImage("cute/TreeShort");
while (x < 400) {
image(grass, x, 303);
image(tree, x, 288);
x += 100;
}
```

Reproduce the supplied loop in the browser-based live editor and inspect the loop-protection path. Confirm how this code bypasses the protector; done means the browser remains responsive and displays the infinite-loop error instead of freezing.

Written by the indexing model from the issue text.