Added 0 String Length Check on address_type.ex before decoding.

[prix-uniris]

Description

At the moment, when an empty string is provided to graphql_schema, It was causing an error in ae-node side since, "" can be decoded but it's not a valid address which is not check in Crypto.valid_address/1. To solve this, added a 0 string length check before decoding the string and progressing forward.

Fixes # (issue)
#362

Type of change

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

How Has This Been Tested?

Added a test in graphql_schema_test.exs

• test "should return error on 0 length address argument"

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