Bug 66425: Avoid a ClassCastException found via oss-fuzz

We try to avoid throwing ClassCastException, but it was possible
to trigger one here with a specially crafted input-file

Should fix https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=61249

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1911501 13f79535-47bb-0310-9956-ffa450edef68

poi-ooxml/src/main/java/org/apache/poi/xwpf/usermodel/XWPFDocument.java

@@ -241,6 +241,7 @@ public class XWPFDocument extends POIXMLDocument implements Document, IBody {
             for (RelationPart rp : getRelationParts()) {
                 POIXMLDocumentPart p = rp.getDocumentPart();
                 String relation = rp.getRelationship().getRelationshipType();
+                try {
                     if (relation.equals(XWPFRelation.STYLES.getRelation())) {
                         this.styles = (XWPFStyles) p;
                         this.styles.onDocumentRead();
@@ -284,6 +285,9 @@ public class XWPFDocument extends POIXMLDocument implements Document, IBody {
                             POIXMLDocumentPart._invokeOnDocumentRead(gp);
                         }
                     }
+                } catch (ClassCastException e) {
+                    throw new IllegalArgumentException("Relation and type of document-part did not match, had relation " + relation + " and type of document-part: " + p.getClass());
+                }
             }
             initHyperlinks();
         } catch (XmlException e) {