reduce calls to FunctionEntry::display logic

parsing/src/parsing.rs

@@ -10,6 +10,8 @@ impl FlatExWrapper {
 
 	const fn new(f: FlatEx<f64>) -> Self { Self { func: Some(f) } }
 
+	const fn is_none(&self) -> bool { self.func.is_none() }
+
 	fn eval(&self, x: &[f64]) -> f64 {
 		self.func
 			.as_ref()
@@ -71,6 +73,8 @@ impl BackingFunction {
 		nth_derivative: None,
 	};
 
+	pub fn is_none(&self) -> bool { self.function.is_none() }
+
 	/// Create new [`BackingFunction`] instance
 	pub fn new(func_str: &str) -> Result<Self, String> {
 		if func_str.is_empty() {

src/function_entry.rs

@@ -383,7 +383,7 @@ impl FunctionEntry {
 	pub fn display(
 		&self, plot_ui: &mut PlotUi, settings: &AppSettings, main_plot_color: Color32,
 	) -> Option<f64> {
-		if self.test_result.is_some() {
+		if self.test_result.is_some() | self.function.is_none() {
 			return None;
 		}