[WS][build.py][clean] Only delete file if it exists

git-svn-id: svn://kolibrios.org@9380 a494cfbc-eb01-0410-851d-a64ba20cac60

_tools/workspace/build.py

@@ -21,6 +21,7 @@ def build():
 def clean():
     output_file_list = parse_tupfile_outputs("Tupfile.lua")
     for output_file in output_file_list:
+        if os.path.exists(output_file):
             os.remove(output_file)
 
 def main(argv):