ghcjs: fix evaluation error in with-packages-wrapper.nix some more

Changed files
+1 -1
pkgs
development
haskell-modules
+1 -1
pkgs/development/haskell-modules/with-packages-wrapper.nix
···
postBuild = ''
. ${makeWrapper}/nix-support/setup-hook
-
${optionalString ghc.isGhcjs ''
cp -r "${ghc}/${ghc.libDir}/"* ${libDir}/
''}
···
postBuild = ''
. ${makeWrapper}/nix-support/setup-hook
+
${optionalString (ghc.isGhcjs or false) ''
cp -r "${ghc}/${ghc.libDir}/"* ${libDir}/
''}