support zero amount transfer with any ringsize

[Slixe]

Description

Support transactions with ringsize 2 with no balance changes.
Support also any transaction with any ringsize that do no balance changes.

This may be useful for messaging systems which use TX to communicate without having to send any token/DERO

Type of change

Please select the right one.

• 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 not work as expected)
• This change requires a documentation update
• This will require a HardFork to be enabled

Which part is impacted ?

• Wallet
• Daemon
• Miner
• Explorer
• Simulator
• Misc (documentation, comments, text...)

Checklist:

• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings

License

Im am contributing & releasing the code under DERO Research License (which can be found here).

[Slixe]

Changed to dev