Bug in hashing process crashes retrieve process

[Eknir]

Summary

When we upload files of with 16519168 < size < 16773119, (with encryption) or 67100000 without encryption, a hash is generated but there are unretrievable
These size generate a Data length of 0 in the metadata, crashing the retrieve process

Steps to reproduce

truncate -s 16154k bee.jpg
curl -F file=@bee.jpg -H "Swarm-Encrypt: true" http://localhost:1633/files

2. Download using the hash generated

The size of problematic files can be calculated on how levels are filled

Expected behavior

Actual behavior

Extra

• Related: Files from specific sizes instantly disappear after encryption swarm#2211
• suspected cause: According to our research, the problem comes from the function "hoistLevels" in hastrie.go, when the target level in the merkle tree is empty after a recursive wrap.
• fix: A proposed quick fix is to launch this function again with the upper level
  adding this at line 138 :

if tlen == 0 {
 return h.hoistLevels(level + 1) 
}