Fix scale function in ftui.helper.js

[tobi01001]

The current scale implementation can lead to return values beyond min/max being specified when the value is out of bounds.

This commit ensures that the boundaries are kept:

export function scale(value, minIn, maxIn, minOut, maxOut) {
  if(value <= minIn) {
	  return minOut;
  }
  else if(value >= maxIn) {
	  return maxOut;
  }
  else
  {	  
	const slope = (minOut - maxOut) / (minIn - maxIn);
	const intercept = slope * -(minIn) + minOut;
	return value * slope + intercept;
  }
}