Fix exponential search for empty collections

[Dhaylight1]

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This fix addresses a boundary bug in the exponential search implementation in exponential_search.py. The function previously accessed sorted_collection[0] without checking whether the list was empty, which caused an IndexError for empty inputs. The fix adds the required empty-list guard so the function correctly returns -1 when the collection is empty, while preserving the expected behavior for valid sorted inputs.

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