fix aws chunked encoding for a empty stream

[sbiscigl]

Issue #, if available:

Incorrect chunked encoding with 0-length underlying stream #3259

Description of changes:

Fixes a issue where if a empty stream was provided to a s3 operation it would write a empty chunk followed by another empty chunk before the trailer resulting in a aws-chunked stream that looked like

0\r\n\r\n0\r\nx-amz-checksum-crc32:AAAAAA==\r\n\r\n

where it should look like

0\r\nx-amz-checksum-crc32:AAAAAA==\r\n\r\n

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• Did a review by yourself.
• Added proper tests to cover this PR. (If tests are not applicable, explain.)
• Checked if this PR is a breaking (APIs have been changed) change.
• Checked if this PR will not introduce cross-platform inconsistent behavior.
• Checked if this PR would require a ReadMe/Wiki update.

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