invalid unicode string issue in tests/main.c

[rayamhk]

For tests/main.c, I got the following message from console:

PDF Error: -22 - Invalid unicode string at position 28 in And special stuff €ÜŽžŠšÁ that áüöä should ÄÜÖß— “”‘’ brea

It seem just for pdf_add_text_wrap() only and the text is missing. I try to replace the €ÜŽžŠšÁ with €ÜŽžšÁ, no error reported and text is shown normally.