Prevent crash in DocumentLoader::dataReceived

Source/core/loader/DocumentLoader.cpp

Index: Source/core/loader/DocumentLoader.cpp
diff --git a/Source/core/loader/DocumentLoader.cpp b/Source/core/loader/DocumentLoader.cpp
index 29bea9bb8661289d9249f586ec79badd2f10b0c2..11f05e28e9220a9a18bbf799a0a7d619418d3174 100644
--- a/Source/core/loader/DocumentLoader.cpp
+++ b/Source/core/loader/DocumentLoader.cpp
@@ -609,7 +609,7 @@ void DocumentLoader::dataReceived(Resource* resource, const char* data, int leng
 
     // If we are sending data to MediaDocument, we should stop here
     // and cancel the request.
-    if (m_frame->document()->isMediaDocument())
+    if (m_frame && m_frame->document()->isMediaDocument())
         cancelMainResourceLoad(ResourceError::cancelledError(m_request.url()));
 }