Possible to attach to no call

[HeyItsJustFelix]

Describe the bug
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To Reproduce
Steps to reproduce the behavior:

1. Make a unit
2. Attatch to nothing

Expected behavior
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Add a check if the list of calls is empty, and if so clicking assign throws an alert

Screenshots
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Desktop (please complete the following information):

• OS: Win 11
• Browser Edge
• Version 4

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context
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