Fix docs cron (#8207)

The change in #8191 to publish daml on sql docs failed because the
versions.json and snapshots.json files don’t exist initially. This PR
fixes that by catching the exception and treating it as an empty file.

changelog_begin
changelog_end

ci/cron/BUILD.bazel

@@ -25,6 +25,7 @@ da_haskell_binary(
         "process",
         "regex-tdfa",
         "safe",
+        "safe-exceptions",
         "semver",
         "split",
         "text",

ci/cron/src/Main.hs

@@ -9,7 +9,7 @@ import System.FilePath.Posix ((</>))
 
 import qualified Control.Concurrent.Async
 import qualified Control.Concurrent.QSem
-import qualified Control.Exception
+import Control.Exception.Safe
 import qualified Control.Monad as Control
 import qualified Control.Monad.Extra
 import qualified Control.Monad.Loops
@@ -113,7 +113,7 @@ build_and_push opts@DocOptions{build} temp versions = do
             putStrLn "Done.")
     where
         restore_sha io =
-            Control.Exception.bracket (init <$> shell "git symbolic-ref --short HEAD 2>/dev/null || git rev-parse HEAD")
+            bracket (init <$> shell "git symbolic-ref --short HEAD 2>/dev/null || git rev-parse HEAD")
                                       (\cur_sha -> shell_ $ "git checkout " <> cur_sha)
                                       (const io)
         push version =
@@ -240,9 +240,13 @@ fetch_gh_versions pred = do
 
 fetch_s3_versions :: DocOptions -> IO Versions
 fetch_s3_versions opts = do
-    dropdown <- fetch "versions.json" False
+    -- On the first run, this will fail so treat it like an empty file.
+    -- We could technically remove the catch later.
+    dropdown <- fetch "versions.json" False `catchIO`
+      (\_ -> pure [])
     -- TODO: read hidden.json after this has run once
-    hidden <- fetch "snapshots.json" True
+    hidden <- fetch "snapshots.json" True `catchIO`
+      (\_ -> pure [])
     return $ versions $ dropdown <> hidden
     where fetch file prerelease = do
               temp <- shell "mktemp"
@@ -317,7 +321,7 @@ download_assets tmp release = do
     manager <- HTTP.newManager TLS.tlsManagerSettings
     tokens <- Control.Concurrent.QSem.newQSem 20
     Control.Concurrent.Async.forConcurrently_ (map uri $ assets release) (\url ->
-        Control.Exception.bracket_
+        bracket_
           (Control.Concurrent.QSem.waitQSem tokens)
           (Control.Concurrent.QSem.signalQSem tokens)
           (do