[bug] Current color should be updated when first palette is created

[milasudril]

Build info

Id: 390707b56b9e263257892ce9e490ecf4 VCS revision id: 6fe88e6f091a4a75e56009db7c7faf15224a62ac Compiler: g++-10 (Ubuntu 10.2.0-5ubuntu1~20.04) 10.2.0

Information about the problem

Bug type: unexpected behavior

Detailed description

When adding first palette to a newly created document, current color is invalid

Step by step procedure to reproduce the problem

1. Create a new document
2. Create a new palette
3. Create a new image
4. Current color is undefined

Expected behavior

When first palette is created, set current color to index 0. Remember to highlight it in the UI.

Platform

• CPU architecture: ANY
• Operating System: ANY
• Amount of RAM: N/A