Check there is only one settings per ContentCompression

This fixes a memory leak with invalid files.

BUG=b/127702368

Change-Id: I815e482189f67c9d715083626829ed79123e94aa
diff --git a/mkvparser/mkvparser.cc b/mkvparser/mkvparser.cc
index 0ab34c4..ace65bd 100644
--- a/mkvparser/mkvparser.cc
+++ b/mkvparser/mkvparser.cc
@@ -4328,6 +4328,12 @@
         return status;
       }
 
+      // There should be only one settings element per content compression.
+      if (compression->settings != NULL) {
+        delete[] buf;
+        return E_FILE_FORMAT_INVALID;
+      }
+
       compression->settings = buf;
       compression->settings_len = buflen;
     }