Fix linear_gradient float precision bug.

This was reported by:
https://github.com/ArthurSonzogni/FTXUI/issues/998

Indeed, the `t` interpolation factor, which is itself interpolated might become
slightly larger than 1.0. This is due to the float precision.
This was supposedly handled, but there was an off-by-one error in the check.

Along the way, fix a bug found by a fuzzer.

Bug: https://github.com/ArthurSonzogni/FTXUI/issues/998
Fixed: https://github.com/ArthurSonzogni/FTXUI/issues/998

src/ftxui/component/dropdown.cpp

@@ -47,7 +47,11 @@ Component Dropdown(DropdownOption option) {
     Element Render() override {
       radiobox.selected =
           util::clamp(radiobox.selected(), 0, int(radiobox.entries.size()) - 1);
-      title_ = radiobox.entries[selected_()];
+      selected_ = util::clamp(selected_(), 0, int(radiobox.entries.size()) - 1);
+
+      if (selected_() >= 0) {
+        title_ = radiobox.entries[selected_()];
+      }
 
       return transform(*open_, checkbox_->Render(), radiobox_->Render());
     }

src/ftxui/component/dropdown_test.cpp

@@ -0,0 +1,34 @@
+// Copyright 2025 Arthur Sonzogni. All rights reserved.
+// Use of this source code is governed by the MIT license that can be found in
+// the LICENSE file.
+
+#include "ftxui/component/component.hpp"  // for Horizontal, Vertical, Button, Tab
+#include "ftxui/component/component_base.hpp"  // for ComponentBase, Component
+#include "ftxui/component/event.hpp"  // for Event, Event::Tab, Event::TabReverse, Event::ArrowDown, Event::ArrowLeft, Event::ArrowRight, Event::ArrowUp
+#include "gtest/gtest.h"  // for AssertionResult, Message, TestPartResult, EXPECT_EQ, EXPECT_FALSE, Test, EXPECT_TRUE, TEST
+
+namespace ftxui {
+
+TEST(DropdownTest, Empty) {
+  std::vector<std::string> list = {};
+  int index = 0;
+  auto dropdown = Dropdown(list, &index);
+
+  dropdown->OnEvent(Event::Return);
+
+  auto screen = Screen(8, 8);
+  auto document = dropdown->Render();
+  Render(screen, document);
+
+  EXPECT_EQ(screen.ToString(),
+            "╭──────╮\r\n"
+            "│↓     │\r\n"
+            "├──────┤\r\n"
+            "│      │\r\n"
+            "│      │\r\n"
+            "│      │\r\n"
+            "│      │\r\n"
+            "╰──────╯");
+}
+
+}  // namespace ftxui

src/ftxui/dom/linear_gradient.cpp

@@ -97,7 +97,11 @@ Color Interpolate(const LinearGradientNormalized& gradient, float t) {
   // Find the right color in the gradient's stops.
   size_t i = 1;
   while (true) {
-    if (i > gradient.positions.size()) {
+    // Note that `t` might be slightly greater than 1.0 due to floating point
+    // precision. This is why we need to handle the case where `t` is greater
+    // than the last stop's position.
+    // See https://github.com/ArthurSonzogni/FTXUI/issues/998
+    if (i >= gradient.positions.size()) {
       const float half = 0.5F;
       return Color::Interpolate(half, gradient.colors.back(),
                                 gradient.colors.back());