Lack of space in binary config dump path doesn't trigger error and hits unrelated assert

Hello,

in a strict container environment i've managed to hit the following bug:

doveconf: Panic: file config-dump-full.c: line 168 (output_blob_size): assertion failed: (output->offset >= blob_size_offset + sizeof(uint64_t))

This was caused due to a very small (2MB) tmpfs for the config location where the binary config is being dumped to and is not reproducible with the config test as no binary config is being written. There is no ENOSPC error being returned, just this assert. Once the tmpfs has been raised the assert wouldn't be hit anymore. IO errors should be reported on all operations.

Dovecot version: 2.4.5 Built from nixpkgs nixos-26.05.11527.2efa67fd26b6

-- Alex D. RedXen System & Infrastructure Administration https://redxen.eu/