When calculating a SEL_TREE for the "c_{i-1} < X < c_i" interval, check if the tree returned for the "-inf < X < c_0" interval is NULL


mysql-test/r/func_in.result:
  Added testcase for bug #24261 "crash when WHERE contains NOT IN ('<negative value>') for unsigned column type"
mysql-test/t/func_in.test:
  Added testcase for bug #24261 "crash when WHERE contains NOT IN ('<negative value>') for unsigned column type"
sql/opt_range.cc:
  When calculating a SEL_TREE for the "c_{i-1} < X < c_i" interval, check if the tree returned for the "-inf < X < c_0" interval is NULL