After the fix for
Bug #55077 Assertion failed: width > 0 && to != ((void *)0), file .\dtoa.c
we no longer try to allocate a string of length 'field_length'
so the asserts are relevant only for ZEROFILL columns.



mysql-test/r/select.result:
  Add test case for Bug#57203
mysql-test/t/select.test:
  Add test case for Bug#57203
sql/field.cc:
  Rewrite the DBUG_ASSERTS on field_length.