Added error propagation in Field access (#500)

boa/src/exec/field/mod.rs

@@ -8,9 +8,7 @@ impl Executable for GetConstField {
     fn run(&self, interpreter: &mut Interpreter) -> ResultValue {
         let mut obj = self.obj().run(interpreter)?;
         if obj.get_type() != Type::Object || obj.get_type() != Type::Symbol {
-            obj = interpreter
-                .to_object(&obj)
-                .expect("failed to convert to object");
+            obj = interpreter.to_object(&obj)?;
         }
 
         Ok(obj.get_field(self.field()))
@@ -21,9 +19,7 @@ impl Executable for GetField {
     fn run(&self, interpreter: &mut Interpreter) -> ResultValue {
         let mut obj = self.obj().run(interpreter)?;
         if obj.get_type() != Type::Object || obj.get_type() != Type::Symbol {
-            obj = interpreter
-                .to_object(&obj)
-                .expect("failed to convert to object");
+            obj = interpreter.to_object(&obj)?;
         }
         let field = self.field().run(interpreter)?;