uninstall: fix when Cellar doesn't exist

Library/Homebrew/cmd/uninstall.rb

@@ -46,9 +46,11 @@ module Homebrew
   ensure
     # If we delete Cellar/newname, then Cellar/oldname symlink
     # can become broken and we have to remove it.
+    if HOMEBREW_CELLAR.directory?
     HOMEBREW_CELLAR.children.each do |rack|
       rack.unlink if rack.symlink? && !rack.resolved_path_exists?
     end
+    end
   end
 
   def rm_pin(rack)