Use safer cast to HasGetChildren

Author: mwilliamson

src/main/java/org/zwobble/mammoth/internal/docx/StatefulBodyXmlReader.java

@@ -772,7 +772,7 @@ private <T extends DocumentElement> Function<DocumentElement, DocumentElement> t
         return element -> {
             if (element instanceof HasChildren) {
                 element = ((HasChildren<DocumentElement>) element).replaceChildren(
-                    Lists.eagerMap(((HasChildren<?>) element).getChildren(), transformElementsOfType(elementClass, transform))
+                    Lists.eagerMap(((HasGetChildren) element).getChildren(), transformElementsOfType(elementClass, transform))
                 );
             }