abort copying on missing assets

lib/CheckDir.hs

@@ -65,7 +65,9 @@ newtype MissingAsset = MissingAsset MissingDep
 
 -- | given this config, should the result be considered to have failed?
 resultIsFatal :: LintConfig' -> DirResult -> Bool
-resultIsFatal config res = maximumLintLevel res > configMaxLintLevel config
+resultIsFatal config res =
+  not (null $ dirresultMissingAssets res)
+  || maximumLintLevel res > configMaxLintLevel config
 
 -- | maximum lint level that was observed anywhere in any map.
 -- note that it really does go through all lints, so don't