bluetooth: mSBC: ignore all-zero packets

This is a workaround for hardware/driver which inserts all-zero packets in what
otherwise looks like a valid mSBC stream.

Part-of: <https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/507>

src/modules/bluetooth/bt-codec-msbc.c

@@ -182,6 +182,16 @@ static size_t encode_buffer(void *codec_info, uint32_t timestamp, const uint8_t
     return MSBC_PACKET_SIZE;
 }
 
+static inline bool is_all_zero(const uint8_t *ptr, size_t len) {
+    size_t i;
+
+    for (i = 0; i < len; ++i)
+        if (ptr[i] != 0)
+            return false;
+
+    return true;
+}
+
 /*
  * We build a msbc frame up in the sbc_info buffer until we have a whole one
  */
@@ -191,6 +201,12 @@ static struct msbc_frame *msbc_find_frame(struct sbc_info *si, ssize_t *len,
     int i;
     uint8_t *p = si->input_buffer;
 
+    /* skip input if it has all zero bytes
+     * this could happen with older kernels inserting all-zero blocks
+     * inside otherwise valid mSBC stream */
+    if (*len > 0 && is_all_zero(buf, *len))
+        *len = 0;
+
     for (i = 0; i < *len; i++) {
         union msbc_h2_id1 id1;