fix(core,edges): use nullish check to fallback to default center

Author: bcakmakoglu

packages/core/src/components/Edges/utils/smoothstep.ts

@@ -85,8 +85,8 @@ function getPoints({
 
   // opposite handle positions, default case
   if (sourceDir[dirAccessor] * targetDir[dirAccessor] === -1) {
-    centerX = center.x || defaultCenterX
-    centerY = center.y || defaultCenterY
+    centerX = center.x ?? defaultCenterX
+    centerY = center.y ?? defaultCenterY
     //    --->
     //    |
     // >---