Merge and adjust a forgotten change to fix this bug.
rb://393 approved by Jimmy Yang
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  r3794 | marko | 2009-01-07 14:14:53 +0000 (Wed, 07 Jan 2009) | 18 lines

  branches/6.0: Allow the minimum length of a multi-byte character to be
  up to 4 bytes. (Bug #35391)

  dtype_t, dict_col_t: Replace mbminlen:2, mbmaxlen:3 with mbminmaxlen:5.
  In this way, the 5 bits can hold two values of 0..4, and the storage size
  of the fields will not cross the 64-bit boundary.  Encode the values as
  DATA_MBMAX * mbmaxlen + mbminlen.  Define the auxiliary macros
  DB_MBMINLEN(mbminmaxlen), DB_MBMAXLEN(mbminmaxlen), and
  DB_MINMAXLEN(mbminlen, mbmaxlen).

  Try to trim and pad UTF-16 and UTF-32 with spaces as appropriate.

  Alexander Barkov suggested the use of cs->cset->fill(cs, buff, len, 0x20).
  ha_innobase::store_key_val_for_row() now does that, but the added function
  row_mysql_pad_col() does not, because it doesn't have the MySQL TABLE object.

  rb://49 approved by Heikki Tuuri
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