Copy value before watching it for mutations in config

If we copy it afterwards, we are going to mutate the copied object.

qutebrowser/config/config.py

@@ -352,12 +352,13 @@ class Config(QObject):
             return obj
 
         value = self._values[name].get_for_pattern(pattern)
+        value = self._maybe_copy(value)
 
         # Watch the returned object for changes if it's mutable.
         if isinstance(value, self.MUTABLE_TYPES):
             self._mutables[name] = (copy.deepcopy(value), value)
 
-        return self._maybe_copy(value)
+        return value
 
     def get_str(self, name, *, pattern=None):
         """Get the given setting as string.