fix a problem with empty scripts

jedi/api.py

@@ -60,7 +60,7 @@ class Script(object):
             warnings.warn("Use path instead of source_path.", DeprecationWarning)
             path = source_path
 
-        lines = source.splitlines()
+        lines = source.splitlines() or ['']
         if source and source[-1] == '\n':
             lines.append('')
 

test/test_api.py

@@ -24,3 +24,7 @@ def test_preload_modules():
     check_loaded('datetime', 'json', 'token')
 
     cache.parser_cache = temp_cache
+
+
+def test_empty_script():
+    assert api.Script('')