fix crash when trying to load and ffi library with an invalid type specification

tests/scryer/ffi.rs

@@ -163,7 +163,22 @@ fn ffi_return_values() {
     // but there is currently no other easy way to get the dynamic library file path as an input into a load_module_test test
     std::env::set_var("ffi_return_values_LIB", dynlib_path);
 
-    // FIXME u32 and u64 have an incorrect result
+    // i8- -42,u8-73,i16- -3054,u16-49374,i32- -200211438,u32-3235819520,i64- -859901580039547648,u64- 859901580039547648,f32-3.1415927410125732,f64-6.283185307179586
+    let expected = format!(
+        "i8- {},u8-{},i16- {},u16-{},i32- {},u32-{},i64- {},u64- {},f32-{},f64-{}",
+        -42,
+        73,
+        -0xBEE,
+        0xC0DE,
+        -0xBEEFBEE,
+        0xC0DEB000u32,
+        -0xBEEFBEE5C0DEB00i64,
+        0xBEEFBEE5C0DEB00u64,
+        std::f32::consts::PI as f64,
+        std::f64::consts::TAU
+    );
+
+    // FIXME all but u8, f32 and f64 are wrong!?!?
     load_module_test(
         "tests-pl/ffi_return_values.pl",
         "i8-214,u8-73,i16-18,u16-222,i32-18,u32-0,i64-0,u64- -4789548415587584,f32-3.1415927410125732,f64-6.283185307179586",