Document that opus_packet_get_nb_frames, etc. can return OPUS_BAD_ARG.

NB they only check for len < 1, not for null data.

include/opus.h

@@ -566,6 +566,7 @@ OPUS_EXPORT OPUS_WARN_UNUSED_RESULT int opus_packet_get_nb_channels(const unsign
   * @param [in] packet <tt>char*</tt>: Opus packet
   * @param [in] len <tt>opus_int32</tt>: Length of packet
   * @returns Number of frames
+  * @retval OPUS_BAD_ARG Insufficient data was passed to the function
   * @retval OPUS_INVALID_PACKET The compressed data passed is corrupted or of an unsupported type
   */
 OPUS_EXPORT OPUS_WARN_UNUSED_RESULT int opus_packet_get_nb_frames(const unsigned char packet[], opus_int32 len) OPUS_ARG_NONNULL(1);
@@ -577,6 +578,7 @@ OPUS_EXPORT OPUS_WARN_UNUSED_RESULT int opus_packet_get_nb_frames(const unsigned
   *                                     This must be a multiple of 400, or
   *                                     inaccurate results will be returned.
   * @returns Number of samples
+  * @retval OPUS_BAD_ARG Insufficient data was passed to the function
   * @retval OPUS_INVALID_PACKET The compressed data passed is corrupted or of an unsupported type
   */
 OPUS_EXPORT OPUS_WARN_UNUSED_RESULT int opus_packet_get_nb_samples(const unsigned char packet[], opus_int32 len, opus_int32 Fs) OPUS_ARG_NONNULL(1);
@@ -586,6 +588,7 @@ OPUS_EXPORT OPUS_WARN_UNUSED_RESULT int opus_packet_get_nb_samples(const unsigne
   * @param [in] packet <tt>char*</tt>: Opus packet
   * @param [in] len <tt>opus_int32</tt>: Length of packet
   * @returns Number of samples
+  * @retval OPUS_BAD_ARG Insufficient data was passed to the function
   * @retval OPUS_INVALID_PACKET The compressed data passed is corrupted or of an unsupported type
   */
 OPUS_EXPORT OPUS_WARN_UNUSED_RESULT int opus_decoder_get_nb_samples(const OpusDecoder *dec, const unsigned char packet[], opus_int32 len) OPUS_ARG_NONNULL(1) OPUS_ARG_NONNULL(2);