fix: dataset layers are not exported correctly

[mimoham24]

Overview

fixing the layer exporting bug

What I've done

encoder now fetches the property values first, if no values found -> fetch values from dataset

What I haven't done

How I tested

export all types "KML, CZML, GeoJSON, SHP"

Which point I want you to review particularly

Memo

[codecov]

Codecov Report

Merging #36 (12401dd) into main (8742dba) will decrease coverage by 0.01%.
The diff coverage is 63.70%.

@@            Coverage Diff             @@
##             main      #36      +/-   ##
==========================================
- Coverage   16.59%   16.58%   -0.02%     
==========================================
  Files         222      222              
  Lines       41150    41186      +36     
==========================================
  Hits         6830     6830              
- Misses      33328    33364      +36     
  Partials      992      992              

Impacted Files	Coverage Δ
pkg/layer/encoding/shp.go	59.54% <46.15%> (-2.86%)	⬇️
pkg/layer/encoding/geojson.go	54.81% <62.50%> (-4.39%)	⬇️
pkg/layer/encoding/kml.go	59.32% <65.85%> (-2.30%)	⬇️
pkg/layer/encoding/czml.go	53.80% <68.42%> (-3.35%)	⬇️

[rot1024]

Changes are ok but I've tried to make the code a little more readable.

[HideBa]

Thanks! 👍