freetdm: make sure gains are not applied to non-voice channels

libs/freetdm/src/ftdm_io.c

@@ -2050,6 +2050,10 @@ FT_DECLARE(ftdm_status_t) ftdm_channel_command(ftdm_channel_t *ftdmchan, ftdm_co
 
 	case FTDM_COMMAND_SET_RX_GAIN:
 		{
+			if (!FTDM_IS_VOICE_CHANNEL(ftdmchan)) {
+				ftdm_log(FTDM_LOG_ERROR, "Cannot set rx gain in non-voice channel of type: %s\n", ftdm_chan_type2str(ftdmchan->type));
+				GOTO_STATUS(done, FTDM_FAIL);
+			}
 			ftdmchan->rxgain = FTDM_COMMAND_OBJ_FLOAT;
 			reset_gain_table(ftdmchan->rxgain_table, ftdmchan->rxgain, ftdmchan->native_codec);
 			if (ftdmchan->rxgain == 0.0) {
@@ -2068,6 +2072,10 @@ FT_DECLARE(ftdm_status_t) ftdm_channel_command(ftdm_channel_t *ftdmchan, ftdm_co
 		break;
 	case FTDM_COMMAND_SET_TX_GAIN:
 		{
+			if (!FTDM_IS_VOICE_CHANNEL(ftdmchan)) {
+				ftdm_log(FTDM_LOG_ERROR, "Cannot set tx gain in non-voice channel of type: %s\n", ftdm_chan_type2str(ftdmchan->type));
+				GOTO_STATUS(done, FTDM_FAIL);
+			}
 			ftdmchan->txgain = FTDM_COMMAND_OBJ_FLOAT;
 			reset_gain_table(ftdmchan->txgain_table, ftdmchan->txgain, ftdmchan->native_codec);
 			if (ftdmchan->txgain == 0.0) {