Automatic indexing of un-indexed files (#1039)

* Downgrade rebuild index dialog from warning to info
* Don't flag index as broken if file is missing, just add it again
* Fix log warning
* Drop the return value in the index checker

novelwriter/guimain.py

@@ -545,7 +545,7 @@ class GuiMain(QMainWindow):
         if self.theIndex.indexBroken:
             self.makeAlert(self.tr(
                 "The project index is outdated or broken. Rebuilding index."
-            ), nwAlert.WARN)
+            ), nwAlert.INFO)
             self.rebuildIndex()
 
         # Make sure the changed status is set to false on things opened