Bug 66425: Avoid a NullPointerException found via oss-fuzz

We try to avoid throwing NullPointerException, 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=61520

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1911863 13f79535-47bb-0310-9956-ffa450edef68

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

@@ -233,7 +233,7 @@ public class XWPFDocument extends POIXMLDocument implements Document, IBody {
                 }
             }
             // Sort out headers and footers
-            if (doc.getDocument().getBody().getSectPr() != null) {
+            if (doc.getDocument().getBody() != null && doc.getDocument().getBody().getSectPr() != null) {
                 headerFooterPolicy = new XWPFHeaderFooterPolicy(this);
             }