add null check for XSLFShape

git-svn-id: https://svn.apache.org/repos/asf/poi/trunk@1868318 13f79535-47bb-0310-9956-ffa450edef68

src/ooxml/testcases/org/apache/poi/xslf/usermodel/TestXSLFShape.java

@@ -83,6 +83,14 @@ public class TestXSLFShape {
         ppt.close();
     }
 
+    @Test
+    public void testProblemFile() throws IOException {
+        try (XMLSlideShow ppt = XSLFTestDataSamples.openSampleDocument("ececapstonespring2012.pptx")) {
+            List<XSLFSlide> slides = ppt.getSlides();
+            assertEquals(24, slides.size());
+        }
+    }
+
     @Test
     public void testCreateShapes() throws IOException {
         XMLSlideShow ppt = new XMLSlideShow();