Fallback to home page for empty bang searches

Bang searches without an actual query (i.e. just searching "!gh") will
now redirect to the home page. I guess people do this for some reason
and don't like that it redirects to the correct bang result URL, but
without an actual search term.

Fixes #595

app/routes.py

@@ -304,8 +304,8 @@ def search():
     search_util = Search(request, g.user_config, g.session_key)
     query = search_util.new_search_query()
 
-    bang = resolve_bang(query=query, bangs_dict=bang_json)
-    if bang != '':
+    bang = resolve_bang(query, bang_json, url_for('.index'))
+    if bang:
         return redirect(bang)
 
     # Redirect to home if invalid/blank search

app/utils/bangs.py

@@ -38,7 +38,7 @@ def gen_bangs_json(bangs_file: str) -> None:
     print('* Finished creating ddg bangs json')
 
 
-def resolve_bang(query: str, bangs_dict: dict) -> str:
+def resolve_bang(query: str, bangs_dict: dict, fallback: str) -> str:
     """Transform's a user's query to a bang search, if an operator is found
 
     Args:
@@ -59,8 +59,13 @@ def resolve_bang(query: str, bangs_dict: dict) -> str:
         if operator not in split_query \
                 and operator[1:] + operator[0] not in split_query:
             continue
-        return bangs_dict[operator]['url'].replace(
-            '{}',
-            query.replace(operator if operator in split_query
-                          else operator[1:] + operator[0], '').strip(), 1)
+
+        bang_query = query.replace(
+            operator if operator in split_query else operator[1:] + operator[0], ''
+        ).strip()
+
+        if bang_query:
+            return bangs_dict[operator]['url'].replace('{}', bang_query, 1)
+        else:
+            return fallback
     return ''