work around parse_qs behavior in python < 3.11

www/lib/kojiweb/util.py

@@ -211,6 +211,12 @@ class FieldStorageCompat(Mapping):
     """Emulate the parts of cgi.FieldStorage that we need"""
 
     def __init__(self, environ):
+        qs = environ.get('QUERY_STRING', '')
+        if not qs:
+            # for python < 3.11, parse_qs will error on a blank string
+            self.data = {}
+            return
+
         data = parse_qs(environ.get('QUERY_STRING', ''), strict_parsing=True,
                         keep_blank_values=True)
         # replace singleton lists with single values