Make negative scaleFactor reverse middle arrow correctly (#3474)

lib/network/modules/components/edges/util/EdgeBase.js

@@ -538,6 +538,7 @@ class EdgeBase {
       }
     }
 
+    if (position === 'middle' && scaleFactor < 0) lineWidth *= -1; // reversed middle arrow
     let length = 15 * scaleFactor + 3 * lineWidth; // 3* lineWidth is the width of the edge.
 
     var xi = arrowPoint.x - length * 0.9 * Math.cos(angle);