fix(grid): zero length grid cell bounds (#6536)

**Problem:**
no gaps cause a null pointer exception

**Fix:**
check for array length and not just a null check.

**Manual Tests:**
I hereby swear that:

- [X] I opened a hydrogen project and it loaded
- [X] I could navigate to various routes in Play mode

editor/src/components/canvas/gap-utils.ts

@@ -223,7 +223,7 @@ export function gridGapControlBoundsFromMetadata(
 
   const gridCellBounds = grid.specialSizeMeasurements.gridCellGlobalFrames
 
-  if (gridCellBounds == null) {
+  if (gridCellBounds == null || gridCellBounds.length == 0) {
     return emptyResult
   }
   const allCellsBound = canvasRectangle({