avformat/imf: fix error CPL root element is absent

Signed-off-by: Pierre-Anthony Lemieux <pal@palemieux.com>
Signed-off-by: Zane van Iperen <zane@zanevaniperen.com>

libavformat/imf_cpl.c

@@ -688,7 +688,7 @@ int ff_imf_parse_cpl_from_xml_dom(xmlDocPtr doc, FFIMFCPL **cpl)
     }
 
     cpl_element = xmlDocGetRootElement(doc);
-    if (xmlStrcmp(cpl_element->name, "CompositionPlaylist")) {
+    if (!cpl_element || xmlStrcmp(cpl_element->name, "CompositionPlaylist")) {
         av_log(NULL, AV_LOG_ERROR, "The root element of the CPL is not CompositionPlaylist\n");
         ret = AVERROR_INVALIDDATA;
         goto cleanup;