LibWeb: Don't crash when querying detached circle element properties

Author: https://github.com/tcl3
Commit: 3518f39b60
Pull-request: https://github.com/SerenityOS/serenity/pull/23687
Reviewed-by: https://github.com/awesomekling

Tests/LibWeb/Text/input/SVG/svg-circle-detached.html

@@ -0,0 +1,10 @@
+<script src="../include.js"></script>
+<script>
+    test(() => {
+        const circleElement = document.createElementNS("http://www.w3.org/2000/svg", "circle");
+        const cx = circleElement.cx;
+        const cy = circleElement.cy;
+        const r = circleElement.r;
+        println("PASS (didn't crash)");
+    });
+</script>