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 cd8f3e51460cf708442b8fabd1d899b480675bbd on bugfix/233_fix_parsing_utf16_inputs into e02af6b1d90d2bef4c042c8b9382b500beb762c9 on develop.