Fix single select dropdown

[whitphx]

Description

gr.Dropdown(multiselect=False) sets the default value as [] of type list. It's a confusing behavior.

The fix is in a04ad54 where the default value is changed from [] to undefined.
As a result, the following value initializer that seems to have not been reached before became effective and the first item of choices is now set as the default value.

gradio/js/dropdown/shared/Dropdown.svelte

Lines 59 to 65 in 0ab6ac5

	} else if (choices.length > 0) {
	old_selected_index = 0;
	selected_index = 0;
	[input_text, value] = choices[selected_index];
	old_value = value;
	old_input_text = input_text;
	}

I think

• setting a list value [] as the default value of a single-select dropdown is obviously a bug.
• but setting the first value of choices instead of None is an opinionated behavior, while I think it's desirable as the user can eliminate the null-checking from the user-defined fn. If it's a problem I will fix it.

For example,
the tone generator example looks like this, where the non-null dropdown value is set by default:

[gradio-pr-bot]

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---

Install Gradio from this PR

pip install https://gradio-pypi-previews.s3.amazonaws.com/bcc1c6c62f0c767bfc9ba40c5e72499d84287af2/gradio-4.44.1-py3-none-any.whl

Install Gradio Python Client from this PR

pip install "gradio-client @ git+https://github.com/gradio-app/gradio@bcc1c6c62f0c767bfc9ba40c5e72499d84287af2#subdirectory=client/python"

Install Gradio JS Client from this PR

npm install https://gradio-npm-previews.s3.amazonaws.com/bcc1c6c62f0c767bfc9ba40c5e72499d84287af2/gradio-client-1.6.0-beta.3.tgz

Use Lite from this PR

<script type="module" src="https://gradio-lite-previews.s3.amazonaws.com/bcc1c6c62f0c767bfc9ba40c5e72499d84287af2/dist/lite.js""></script>

[gradio-pr-bot]

🦄 change detected

This Pull Request includes changes to the following packages.

Package	Version
@gradio/dropdown	minor
gradio	minor

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With the following changelog entry.

Fix single select dropdown

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