Fix potential leak

Fix potential memory leak introduced with bugfix for bug 31449945.

Bug: 36389123
Change-Id: I5a9a3551692d6cba385b45c4c7a465aa377a62b1
(cherry picked from commit a0721999eccd22d900eb6dec7e48f835f28ce999)
diff --git a/media/libstagefright/MPEG4Extractor.cpp b/media/libstagefright/MPEG4Extractor.cpp
index 00215c9..885f2cb 100644
--- a/media/libstagefright/MPEG4Extractor.cpp
+++ b/media/libstagefright/MPEG4Extractor.cpp
@@ -2739,8 +2739,10 @@
                     int32_t delay, padding;
                     if (sscanf(mLastCommentData,
                                " %*x %x %x %*x", &delay, &padding) == 2) {
-                        if (mLastTrack == NULL)
+                        if (mLastTrack == NULL) {
+                            delete[] buffer;
                             return ERROR_MALFORMED;
+                        }
 
                         mLastTrack->meta->setInt32(kKeyEncoderDelay, delay);
                         mLastTrack->meta->setInt32(kKeyEncoderPadding, padding);