Overwriting small file with big file breaks syncing / access to file

### Step 1: Please describe your environment

* ZeroNet version: latest py3
* Operating system: Debian

### Step 2: Describe the problem:

Replacing a file which was fitting "small file limit" with a file that doesn't leads to file being unavailable on other nodes (at least on proxies). No `.piecemap.msgpack` is generated, even after deleting the file, signing changes and bringing it back; so i suspect that's the cause of the problem on remote nodes.

#### Steps to reproduce:

1. Add small optional file (lets say "file.bin") to a site and sign changes
2. Replace small "file.bin" with a big "file.bin" and sign changes
3. Try to access "file.bin" from other nodes

Proxies result in either time out or not found error