Tool call completion will not auto trigger request if message content isn't empty

[yyjhao]

Description

This line: https://github.com/vercel/ai/blob/main/packages/react/src/use-chat.ts#L351

breaks some agents that has non-empty message with a tool call. The message that the agent has is not necessarily the result of the tool call, it may just be the agent saying that they are going to use a tool. It breaks for me with sync client tool use.

Code example

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AI provider

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Additional context

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