### **Environment**:

Your OpenProject Version: 12.0.1

### **Steps to reproduce:**

1. Create a work package custom field, tick 'Used as a filter'

2. Create a work package query using this custom field as a filter

3. Edit the custom field and uncheck 'Used as a filter'

4. Open the work package query and try to export as, say, XLS


### **Actual Behavior**

A red error message with "Bad request."

### **Expected Behavior**

The export should let the user know this is due to the no longer available field in filter query.
The filter field is displayed with a Begin of the insertionredEnd of the insertion Begin of the deletion readEnd of the deletion warning string and the option for the user to remove it from their filters
On saving/"saving as" the query, the invalid filter field is removed (instead of crashing angular)

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