BUG: Apply patch from issue #6006.

Source/cmInstallCommand.cxx

@@ -925,7 +925,8 @@ cmInstallCommand::HandleDirectoryMode(std::vector<std::string> const& args)
         }
 
       // Make sure the name is a directory.
-      if(!cmSystemTools::FileIsDirectory(dir.c_str()))
+      if(cmSystemTools::FileExists(dir.c_str()) &&
+         !cmSystemTools::FileIsDirectory(dir.c_str()))
         {
         cmOStringStream e;
         e << args[0] << " given non-directory \""