libFLAC: Remove un-needed assert

This asset was firing when the build was configured with --enable-debug
and the flac executable was then run under American Fuzzy Lop. Removing
the assert did not cause any other problems, even under AFL.
diff --git a/src/libFLAC/metadata_object.c b/src/libFLAC/metadata_object.c
index a799bf8..33a2b55 100644
--- a/src/libFLAC/metadata_object.c
+++ b/src/libFLAC/metadata_object.c
@@ -567,7 +567,6 @@
 					return 0;
 				}
 				if(object->data.vorbis_comment.num_comments == 0) {
-					FLAC__ASSERT(0 == object->data.vorbis_comment.comments);
 					to->data.vorbis_comment.comments = 0;
 				}
 				else {