Fixed that the Column_definition::pack_flag member corresponding to
ROW-type SP variables and their fields was not properly initialized.
This lead to sporadic test failures. Valgrind complained about jumps
depending on uninitialized value in VALGRIND builds.

This patch makes sure that sp_head::fill_spvar_definition() is always
called for ROW variables and their fields.

Additionally, fixed that a function with a scalar parameter
erroneously acceptes ROWs with one fields. Now an error is returned.