gpg: Fix export in mode1003 when cache nonce is used.
* g10/call-agent.c (agent_export_key): Add missing space.
Unfortunately I only tested with a offline primary key and thus no
cache nonce was used.
- GnuPG-bug-id: T7315
- Fixes-commit: e5473262e88473a101241e7b4860882ebeb1ed97