[3924] Fix small bugs in fx diagram editor

Fixes various minor things that came up when updating the security plugin.

org.fortiss.tooling.common.ui/src/org/fortiss/tooling/common/ui/javafx/lwfxef/visual/elliptic/EllipticBorderLocation.java

@@ -10,8 +10,6 @@
 package org.fortiss.tooling.common.ui.javafx.lwfxef.visual.elliptic;
 
 import static java.lang.Math.atan2;
-import static java.lang.Math.cos;
-import static java.lang.Math.sin;
 import static java.util.Objects.requireNonNull;
 
 import org.fortiss.tooling.common.ui.javafx.lwfxef.DiagramCoordinate;
@@ -53,14 +51,23 @@ public final class EllipticBorderLocation {
 	/**
 	 * Returns the location computed from this {@link EllipticBorderLocation} relative to the
 	 * ellipse center.
+	 * TODO(JE): leads to java.lang.ArithmeticException: / by zero if cos is 0. What is the
+	 * difference to the existing code? Why is an adaption needed?
 	 */
 	public DiagramCoordinate getLocation() {
-		double rw = radiuses.getWidth();
-		double rh = radiuses.getHeight();
 		double angle = Math.PI * angleInDegree / 180;
-		double x = rw - correction.getWidth() / 2 + rw * cos(angle);
-		double y = rh - correction.getHeight() / 2 - rh * sin(angle);
-		return new DiagramCoordinate(x, y);
+		double rh = radiuses.getWidth();
+		double rv = radiuses.getHeight();
+		DiagramCoordinate middle = new DiagramCoordinate(rh, rv);
+		double cos = Math.cos(angle);
+		double sin = Math.sin(angle);
+		double tan = (sin / cos);
+		// Division by zero will result in tan being Infinity,
+		// which gives the right results for x and y.
+		double x = rh * rv / Math.sqrt(rv * rv + rh * rh * tan * tan);
+		double y = rh * rv * Math.signum(tan) / Math.sqrt(rv * rv / (tan * tan) + rh * rh);
+		return middle.add(x * Math.signum(cos), -y * Math.signum(cos))
+				.subtract(correction.getWidth() / 2.0, correction.getHeight() / 2.0);
 	}
 
 	/**