Don't CHECK if the source can't be started

Bug: 19779574
Bug: 31156921
Change-Id: I770619949ed211dab301ee3da10069d319279715
diff --git a/media/libstagefright/NuMediaExtractor.cpp b/media/libstagefright/NuMediaExtractor.cpp
index a669dca..276d731 100644
--- a/media/libstagefright/NuMediaExtractor.cpp
+++ b/media/libstagefright/NuMediaExtractor.cpp
@@ -305,7 +305,10 @@
 
     sp<IMediaSource> source = mImpl->getTrack(index);
 
-    CHECK_EQ((status_t)OK, source->start());
+    status_t ret = source->start();
+    if (ret != OK) {
+        return ret;
+    }
 
     mSelectedTracks.push();
     TrackInfo *info = &mSelectedTracks.editItemAt(mSelectedTracks.size() - 1);