Fix delay effect on Teensy 3.5 & 3.6

effect_delay.cpp

 	tail = tailindex;
 	if (++head >= DELAY_QUEUE_SIZE) head = 0;
 	if (head == tail) {
-		release(queue[tail]);
+		if (queue[tail] != NULL) release(queue[tail]);
 		if (++tail >= DELAY_QUEUE_SIZE) tail = 0;
 	}
 	queue[head] = receiveReadOnly();
 	if (count > maxblocks) {
 		count -= maxblocks;
 		do {
-			release(queue[tail]);
-			queue[tail] = NULL;
+			if (queue[tail] != NULL) {
+				release(queue[tail]);
+				queue[tail] = NULL;
+			}
 			if (++tail >= DELAY_QUEUE_SIZE) tail = 0;
 		} while (--count > 0);
 	}

effect_delay.h

 		maxblocks = max;
 	}
 	uint8_t activemask;   // which output channels are active
-	uint8_t headindex;    // head index (incoming) data in quueu
-	uint8_t tailindex;    // tail index (outgoing) data from queue
-	uint8_t maxblocks;    // number of blocks needed in queue
+	uint16_t headindex;    // head index (incoming) data in quueu
+	uint16_t tailindex;    // tail index (outgoing) data from queue
+	uint16_t maxblocks;    // number of blocks needed in queue
+#if DELAY_QUEUE_SIZE * AUDIO_BLOCK_SAMPLES < 65535
 	uint16_t position[8]; // # of sample delay for each channel
+#else
+	uint32_t position[8]; // # of sample delay for each channel
+#endif
 	audio_block_t *queue[DELAY_QUEUE_SIZE];
 	audio_block_t *inputQueueArray[1];
 };