API: fix transaction_chain when the paging_address == genesis_address

[bchamagne]

Description

When querying a chain with paging_state = genesis we should act as if paging_state is nil

Example of broken behaviour (testnet data)

query {
 transactionChain(
    address: "00006AF4C3AE64D435DA162B27918D6BE3AF8610494E3021148709BBE11A5520334C",
    pagingAddress: "00006AF4C3AE64D435DA162B27918D6BE3AF8610494E3021148709BBE11A5520334C"
  ) {
		address
    
  }
}

This should reply the same thing as the following query

query {
 transactionChain(
    address: "00006AF4C3AE64D435DA162B27918D6BE3AF8610494E3021148709BBE11A5520334C"
  ) {
		address
  }
}

It currently return empty (instead of 2 txs)

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Unit test + manual test

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules