Avoid NPE with malformed anchors in slideshow files

poi-scratchpad/src/main/java/org/apache/poi/hslf/usermodel/HSLFGroupShape.java

@@ -210,6 +210,10 @@ implements HSLFShapeContainer, GroupShape<HSLFShape,HSLFTextParagraph> {
         if(clientAnchor == null) {
             LOG.atInfo().log("EscherClientAnchorRecord was not found for shape group. Searching for EscherChildAnchorRecord.");
             EscherChildAnchorRecord rec = getEscherChild(EscherChildAnchorRecord.RECORD_ID);
+            if (rec == null) {
+                throw new IllegalStateException("Cannot get anchor, neither had an EscherClientAnchorRecord nor an EscherChildAnchorRecord");
+            }
+
             x1 = rec.getDx1();
             y1 = rec.getDy1();
             x2 = rec.getDx2();