Restore cursor shape on exit. (#793) (#794)

Fixed: https://github.com/ArthurSonzogni/FTXUI/issues/792

src/ftxui/component/resizable_split.cpp

@@ -42,7 +42,8 @@ class ResizableSplitBase : public ComponentBase {
       return true;
     }
 
-    if (event.mouse().IsPressed() &&
+    if (event.mouse().button == Mouse::Left &&
+        event.mouse().motion == Mouse::Pressed &&
         separator_box_.Contain(event.mouse().x, event.mouse().y) &&
         !captured_mouse_) {
       captured_mouse_ = CaptureMouse(event);