Merge pull request #1 from gzb1128/test

fix #3646, forcefully change unsupported input to strings

Author: gzb1128

packages/less/bin/lessc

@@ -180,7 +180,9 @@ function render() {
       var filename = sourceMapOptions.sourceMapFullFilename;
       ensureDirectory(filename);
 
+      //To fix https://github.com/less/less.js/issues/3646
       output=output.toString();
+      
       fs.writeFile(filename, output, 'utf8', function (err) {
         if (err) {
           var description = 'Error: ';