libdatasource: fix null dereference

mediaHTTP can be NULL when failed to make http connection
from http service, and then mediaHTTP->connect() will crash.
check if mediaHTTP is NULL before calling mediaHTTP->connect().

Bug: 186381982
Change-Id: I936baf9fbbb2001f8f48f0f1c15f6bc08513600a
Test: http streaming ut
diff --git a/media/libdatasource/DataSourceFactory.cpp b/media/libdatasource/DataSourceFactory.cpp
index bb6a08c..f91e3ea 100644
--- a/media/libdatasource/DataSourceFactory.cpp
+++ b/media/libdatasource/DataSourceFactory.cpp
@@ -65,6 +65,9 @@
         sp<HTTPBase> mediaHTTP = httpSource;
         if (mediaHTTP == NULL) {
             mediaHTTP = static_cast<HTTPBase *>(CreateMediaHTTP(httpService).get());
+            if (mediaHTTP == NULL) {
+                return NULL;
+            }
         }
 
         String8 cacheConfig;