OpusHeader: Add error checks for channel count

Add error check for invalid number of channel count in
WriteOpusHeader().

Bug: 181155583
Test: test in bug
Change-Id: I4b96f1a537103beaf1a3298943b5a5e1893488aa
diff --git a/media/libstagefright/foundation/OpusHeader.cpp b/media/libstagefright/foundation/OpusHeader.cpp
index 784e802..30d0ae6 100644
--- a/media/libstagefright/foundation/OpusHeader.cpp
+++ b/media/libstagefright/foundation/OpusHeader.cpp
@@ -146,6 +146,10 @@
 int WriteOpusHeader(const OpusHeader &header, int input_sample_rate,
                     uint8_t* output, size_t output_size) {
     // See https://wiki.xiph.org/OggOpus#ID_Header.
+    if (header.channels < 1 || header.channels > kMaxChannels) {
+        ALOGE("Invalid channel count: %d", header.channels);
+        return -1;
+    }
     const size_t total_size = kOpusHeaderStreamMapOffset + header.channels;
     if (output_size < total_size) {
         ALOGE("Output buffer too small for header.");