add failing test highlighting panic on invalid UTF-8 cstr

Signed-off-by: Thierry Marianne <thierry@marianne.io>

tests-pl/ffi_utf8_panic.pl

@@ -0,0 +1,16 @@
+:- use_module(library(os)).
+:- use_module(library(ffi)).
+
+init :-
+    read(Body),
+    term_variables(Body, [LIB]),
+    Body,
+    use_foreign_module(LIB, [
+        'ffi_invalid_utf8_cstr'([], cstr)
+    ]).
+
+test :-
+    ffi:'ffi_invalid_utf8_cstr'(Str),
+    write(Str), nl.
+
+:- initialization((init,test)).