Two minor bugfixes to the workflow

[elinscott]

This PR fixes two issues:

• proper catching of the case where nscf is not provided as an input to a Wannier90WorkChain
• replaces uses of kind.symbol with of kind.name in Wannier90BaseWorkChain (required when atoms have tags)

[aiida-cla-bot]

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I have read the CLA Document and I hereby accept the CLA

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1 out of 2 committers have signed the CLA.
✅ (elinscott)[https://github.com/elinscott]
❌ @mikibonacci
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[elinscott]

I have read the CLA Document and I hereby accept the CLA