Hide `Add Task` button if current relation is empty to fix #128

[Zoha131]

Description

I have used @ViewBuilder attribute to pass the appropriate View to the navigationBarItems(trailing:) method. Before collecting data from the server the id of currentRelation is 0 and if the user doesn't have any Relation then the server response for id would be nil. This is why I have checked both of the conditions.

Fixes #128

Type of Change:

• Code
• User Interface

Code/Quality Assurance Only

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

How Has This Been Tested?

I have manually tested the screens.

Has Relation	No Relation

Checklist:

Delete irrelevant options.

• [x] My PR follows the style guidelines of this project
• [x] I have performed a self-review of my own code or materials

Code/Quality Assurance Only

• [x] My changes generate no new warnings
• [x] New and existing unit tests pass locally with my changes

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