Limit selling buildings during siege/invasion

As it is right now for this situation:

• A is invading one of B's systems
• B is not confident being able to hold onto or quickly retake the system

B can sell off all of its system's improvements during the siege, thus greatly diminishing the gains A will have as A must rebuild the system to make it useful again.

This is, of course, a perfectly valid and historically accurate war action. However given that a siege/invasion is currently occurring, B should only be able to sell off X amount of improvements per turn, or perhaps get reduced/no gains from the selling.

This would be keeping in line with the idea that a besieged/invaded system cannot have its residents shipped off via the space station.