Fix trap handling bug on Windows and add test

lib/runtime-core-tests/tests/exception_handling.rs

@@ -0,0 +1,21 @@
+use wasmer_runtime_core::{compile_with, imports};
+use wasmer_runtime_core_tests::{get_compiler, wat2wasm};
+
+#[test]
+fn exception_handling_works() {
+    const MODULE: &str = r#"
+(module
+  (func (export "throw_trap")
+    unreachable
+  ))
+"#;
+
+    let wasm_binary = wat2wasm(MODULE.as_bytes()).expect("WAST not valid or malformed");
+    let module = compile_with(&wasm_binary, &get_compiler()).unwrap();
+
+    let imports = imports! {};
+    for _ in 0..2 {
+        let instance = module.instantiate(&imports).unwrap();
+        assert!(instance.call("throw_trap", &[]).is_err());
+    }
+}

lib/win-exception-handler/exception_handling/exception_handling.c

@@ -59,6 +59,7 @@ uint8_t callProtected(trampoline_t trampoline,
     // install exception handler
     if (exceptionHandlerInstalled == FALSE) {
         exceptionHandlerInstalled = TRUE;
+        alreadyHandlingException = FALSE;
         handle = AddVectoredExceptionHandler(CALL_FIRST, exceptionHandler);
     }
 
@@ -86,4 +87,4 @@ uint8_t callProtected(trampoline_t trampoline,
 
     removeExceptionHandler();
     return FALSE;
-}
+}