ExtractImagesController. null checks

src/main/java/stirling/software/SPDF/controller/api/misc/ExtractImagesController.java

@@ -140,6 +140,9 @@ public class ExtractImagesController {
             Set<Integer> processedImages,
             ZipOutputStream zos)
             throws IOException {
+        if(page.getResources() == null || page.getResources().getXObjectNames() == null) {
+    		return;
+    	}
         for (COSName name : page.getResources().getXObjectNames()) {
             if (page.getResources().isImageXObject(name)) {
                 PDImageXObject image = (PDImageXObject) page.getResources().getXObject(name);