Server crashed in some cases when a query required a MIN/MAX
agrregation for a 'ucs2' field. 
In these cases  the aggregation caused calls of the function
update_tmptable_sum_func that indirectly invoked 
the method Item_sum_hybrid::min_max_update_str_field() 
containing a call to strip_sp for a ucs2 character set.
The latter led directly to the crash as it used my_isspace
undefined for the ucs2 character set.
Actually the call of strip_sp is not needed at all in this
situation and has been removed by the fix.