Fix pure virtual function call v2

[adrian-cojocaru]

Follow-up to #3979.

VectorTile class has a TileLoader member that goes out of scope in the base class, after ~VectorMVTTile / ~VectorMLTTile is called and can still handle requests before its parent gets destroyed. Incoming requests in this time frame resolve loadData calls to it's pure virtual definition.

• This PR enforces the TileLoader destruction in the derived classes
• Since the object is being destroyed (tile was marked as obsolete), an alternative fix is to change VectorTile::loadData to an empty implementation and ignore the response data.

[github-actions]

Bloaty Results 🐋

Compared to main

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0% +57.8Ki  +0.0% +12.9Ki    TOTAL

Full report: https://maplibre-native.s3.eu-central-1.amazonaws.com/bloaty-results/pr-3996-compared-to-main.txt

Compared to d387090 (legacy)

    FILE SIZE        VM SIZE    
 --------------  -------------- 
   +47% +54.9Mi  +451% +26.9Mi    TOTAL

Full report: https://maplibre-native.s3.eu-central-1.amazonaws.com/bloaty-results/pr-3996-compared-to-legacy.txt

[github-actions]

Bloaty Results (iOS) 🐋

Compared to main

    FILE SIZE        VM SIZE    
 --------------  -------------- 
  +0.0% +1.74Ki  +0.1% +16.0Ki    TOTAL

Full report: https://maplibre-native.s3.eu-central-1.amazonaws.com/bloaty-results-ios/pr-3996-compared-to-main.txt