Create database fails when an empty createDatabase folder is present

**Describe the bug**
If an empty createDatabase folder exists, grate does not fall back to the default creation script, so no database is created.

**To Reproduce**
Create all default folders for grate, leaving createDatabase empty. Attempt to run a migration targeting a database that doesn't exist.

**Expected behavior**
The default creation script to be used (or clearer docs about which folders can be safely left empty)

**Desktop (please complete the following information):**
- OS: Windows 11
- Version: 1.7.4

**Additional context**
This isn't really a huge issue, as I mostly stumbled into it because I created the entire folder schema while testing the tool. I think making it work like the other folders (where they are ignored if empty) or clearly documenting that it is an exception would be fine.