api: Fix resetting a query title

When removing a query title, make sure it's represented as null in the
database, and not as an empty string. Otherwise it'll be impossible to
click in the various lists and otherwise break stuff.

Change-Id: I8f4d22d99e9a692105c23a9ad40214eb52923a61

Author: supertassu

quarry/web/api.py

@@ -74,7 +74,10 @@ def api_set_meta() -> Tuple[Union[str, Response], int]:
         return "Authorization denied", 403
 
     if "title" in request.form:
-        query.title = request.form["title"]
+        title = request.form["title"]
+        if not title.strip():
+            title = None
+        query.title = title
     if "published" in request.form:
         query.published = request.form["published"] == "1"
     if "description" in request.form: