fix(validation): Remove css-classes if mouse moves directly to different handle.

If two handles are next to each other or overlap it is possible for the
mouse-cursor to move from one handle to the other without a
mouse-move-event being fired where isHoveringHandle is false.

Thus, the valid and connecting css-classes were not removed from the
handle.

This commit fixes this.

src/components/Handle/handler.ts

@@ -153,6 +153,7 @@ export function handleMouseDown({
     }
 
     if (connection.source !== connection.target && elementBelow) {
+      resetRecentHandle(recentHoveredHandle);
       recentHoveredHandle = elementBelow;
       elementBelow.classList.add('react-flow__handle-connecting');
       elementBelow.classList.toggle('react-flow__handle-valid', isValid);