🐛 OOXML: Fix regression introduced in 271f1e6

If a part exists without a linked relation, the deletePart method
throws an exception: `throw new IllegalArgumentException("partName");`

This is not the expected behaviour here: malformed files, or partly
sanitized files match this pattern.

Instead, we check if the relationship exists and is in the package.

module/module-office/src/main/java/xyz/docbleach/modules/ooxml/OOXMLBleach.java

@@ -176,11 +176,28 @@ void sanitize(IBleachSession session, OPCPackage pkg, PackagePart part) throws I
         ContentType type = part.getContentTypeDetails();
         if (isForbiddenType(type) || isStrangeContentType(type)) {
             LOGGER.debug(SUSPICIOUS_OOXML_FORMAT, contentType, part.getPartName(), part.getSize());
-            pkg.deletePart(part.getPartName());
+            deletePart(pkg, part.getPartName());
             session.recordThreat("Dynamic content", SEVERITY.HIGH);
         }
     }
 
+    /**
+     * Delete the part with the specified name and its associated relationships part if one exists.
+     * <p>
+     * Unlike {@link OPCPackage#deletePart(PackagePartName)}, this checks if the relationship exists
+     * before trying to remove it, instead of throwing an exception.
+     *
+     * @param partName Name of the part to delete
+     */
+    private void deletePart(OPCPackage pkg, PackagePartName partName) {
+        pkg.removePart(partName);
+
+        PackagePartName relationshipPartName = PackagingURIHelper.getRelationshipPartName(partName);
+        if (relationshipPartName != null && pkg.containPart(relationshipPartName)) {
+            pkg.removePart(relationshipPartName);
+        }
+    }
+
     boolean isForbiddenType(ContentType type) {
         String full_type = type.toString(false);