Fix lifetime of CString uses
Fix lifetime of CString uses

See "warning" in the documentation under
https://doc.rust-lang.org/std/ffi/struct.CString.html#method.as_ptr

Solves symptoms like e.g.:
Error opening data file /usr/share/tesseract-ocr/tessdata/NULL.traineddata

antimatter15/tesseract-rs,antimatter15/tesseract-rs