Ticket 49958: extended search fail to match entries
    
    Bug Description:
    	During an extended search, a structure is created for each filter component.
    	The structure contains the keys generated from the assertion and using the given
    	matching rule indexer.
    	Later the keys will be compared (with the MR) with keys generated from the
    	attribute values of the candidate entries.
    	The bug is that parsing the assertion, instead of removing the heading spaces
    	the routine clear the assertion that is empty. So the generated keys is NULL.
    
    Fix Description:
    	The fix consists to only remove heading spaces
    
    https://pagure.io/389-ds-base/issue/49958
    
    Reviewed by: Mark Reynolds
    
    Platforms tested: F27
    
    Flag Day: no
    
    Doc impact: no