fix a crash in base64 buffer pool (#8925)
fix a crash in base64 buffer pool (#8925)

looks like 1024 buffer size is not enough in
all situations, use 8192 instead which
can satisfy all the rare situations that
may arise in base64 decoding.
harshavardhana/minio,vadmeste/minio,minio/minio,harshavardhana/minio,balamurugana/minio,NitishT/minio,aead/minio,harshavardhana/minio,donatello/minio,harshavardhana/minio,aead/minio,krisis/minio,harshavardhana/minio,fwessels/minio,aead/minio,krisis/minio,aead/minio,fwessels/minio,NitishT/minio,vadmeste/minio,harshavardhana/minio,fwessels/minio,donatello/minio,aead/minio,minio/minio,harshavardhana/minio,harshavardhana/minio,NitishT/minio,NitishT/minio,aead/minio,aead/minio,balamurugana/minio,fwessels/minio,aead/minio