forgotten set status on Problem type

as remindered at https://github.com/kataras/iris/issues/1335#issuecomment-521319721


Former-commit-id: 7fc7742c5c3374718fbf39530c45fa068b5d433a

context/context.go

@@ -3201,12 +3201,14 @@ func (ctx *context) Problem(v interface{}, opts ...JSON) (int, error) {
 		options.Indent = "  "
 	}
 
-	ctx.contentTypeOnce(ContentJSONProblemHeaderValue, "")
-
 	if p, ok := v.(Problem); ok {
 		p.updateTypeToAbsolute(ctx)
+		code, _ := p.getStatus()
+		ctx.StatusCode(code)
 	}
 
+	ctx.contentTypeOnce(ContentJSONProblemHeaderValue, "")
+
 	return ctx.JSON(v, options)
 }