Fix bug with calling a pure function method-call style.

tests/method_call.rs

@@ -38,3 +38,12 @@ fn test_method_call() -> Result<(), Box<EvalAltResult>> {
 
     Ok(())
 }
+
+#[test]
+fn test_method_call_style() -> Result<(), Box<EvalAltResult>> {
+    let mut engine = Engine::new();
+
+    assert_eq!(engine.eval::<INT>("let x = -123; x.abs(); x")?, -123);
+
+    Ok(())
+}