Fix TIFFTAG_RESOLUTIONUNIT handling.

If there is no TIFFTAG_RESOLUTIONUNIT record, the value of resUnit
should be RESUNIT_INCH and not RESUNIT_NONE.

Task-number: QTBUG-22322
Change-Id: Iedc3120d331308cea9f743de2e4d61cb52cb14c3
(Cherry picked from commit
qtimageformats/44ea4280b20179eea5520fd1ef5ac814c528c45e.)
Reviewed-by: aavit <eirik.aavitsland@digia.com>