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Since qp uses panics as an error mechanism, the top-level functions
recover those errors to return them normally.

However, this blows up if, internally, an ipld.Node implementation
panics with a value whose type is not error. For example, with:

	panic("some panic message")

One gets:

	panic: some panic message [recovered]
		panic: interface conversion: string is not error: missing method Error

Fix this by having a fallback for non-error panic values.