Sped up the initial scanning for annexed files by 15%

Avoids database querying overhead when the database is newly created.

In the large repository where git-annex init took 24 seconds, this sped it
up to 20.47 seconds, a speedup of around 15%.

Sponsored-by: Dartmouth College's DANDI project

Database/Keys/SQL.hs

@@ -1,6 +1,6 @@
 {- Sqlite database of information about Keys
  -
- - Copyright 2015-2021 Joey Hess <id@joeyh.name>
+ - Copyright 2015-2022 Joey Hess <id@joeyh.name>
  -
  - Licensed under the GNU AGPL version 3 or higher.
  -}
@@ -88,6 +88,15 @@ addAssociatedFile k f = queueDb $
   where
 	af = SFilePath (getTopFilePath f)
 
+-- Faster than addAssociatedFile, but only safe to use when the file
+-- was not associated with a different key before, as it does not delete
+-- any old key.
+newAssociatedFile :: Key -> TopFilePath -> WriteHandle -> IO ()
+newAssociatedFile k f = queueDb $
+	void $ insert $ Associated k af
+  where
+	af = SFilePath (getTopFilePath f)
+
 {- Note that the files returned were once associated with the key, but
  - some of them may not be any longer. -}
 getAssociatedFiles :: Key -> ReadHandle -> IO [TopFilePath]