fixed parsing UTF-16 encoded inputs which do not end with a surrogate…

[fktn-k]

This PR fixed a bug in parsing UTF-16 encoded inputs reported in #233.
Also, the test suite has been modified to ensure the change works as expected.

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[coveralls]

coverage: 100.0%. remained the same
when pulling cd8f3e5 on bugfix/233_fix_parsing_utf16_inputs
into e02af6b on develop.