Don't assume view.sel() isn't empty in is_js_file

Issue #133

Author: marijnh

tern.py

@@ -13,7 +13,7 @@
 is_st2 = int(sublime.version()) < 3000
 
 def is_js_file(view):
-  return view.score_selector(sel_end(view.sel()[0]), "source.js") > 0
+  return len(view.sel()) > 0 && view.score_selector(sel_end(view.sel()[0]), "source.js") > 0
 
 files = {}
 arghints_enabled = False