Correct MetaData MIN+MAX on SV change

[jp112sdl]

Description

When changing the type of a system variable, the MetaData() of MIN and MAX are not getting cleared, if the system variable has not a min-to-max range.

This patch will always set the MetaData(MIN) and MetaData(MAX) to null first.

Related Issue

https://homematic-forum.de/forum/viewtopic.php?f=65&t=77676&start=20#p754163

Types of changes

• Docs change / refactoring / dependency upgrade
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Alternate Designs

Possible Drawbacks

Verification Process

Release Notes

Contributing checklist

• My code follows the code style of this project.
• I have read the CONTRIBUTING and LICENSE document.
• I fully agree to distribute my changes under Apache 2.0 license.

[jens-maus]

Changed your PR to better use RemoveMetaData() instead of using 'null' because using null will just set it to null and not remove it!

[jp112sdl]

Didn't know the presence of RemoveMetaData...
Requesting MIN or MAX gave back null. So I thought it simply has to be set to null.

[MichaelN0815]

Wir müssen da noch mehr "resetten":

Das sind "Überbleibsel" wenn die SV vorher Typ Logik oder Typ Werteliste war.