Hex files with Filesystem extension crash on Microbit, works in simulator

[Raekon]

Describe the bug
A clear and concise description of what the bug is.
when use the 'Filesystem' extension in Makecode, the simulator works fine, but when transfered to the Microbit, the program crashes with sad-face-code 030.

Even if I include just a single block of "File", this happens.
For instance, the supplied demo program of "accelerator measuring" on the extension page does this.

Desktop (please complete the following information):

• OS: Win 10
• MAkecode App
• Version :version makecode.microbit.org: 2.0.6
  version Microsoft MakeCode: 5.15.12
  version microbit runtime: pxtgc-0

I have the latest Firmware on the 'bit.

-Morten

[abchatra]

Transferred to https://github.com/Microsoft/pxt-filesystem