Problem:
uint32 multiplication overflow happened during
calculation of proper_length in case of a big n_points value,
so the condition "len < proper_length" did not detect out-of-range errors.
            
Fix:
Adding constants Gis_multi_point::max_n_points and
Gis_line_string::max_n_points and checking that n_points
value in the input WKB data do not exceed max_n_points.

@ internal/mysql-test/suite/i_main/r/gis.result
@ internal/mysql-test/suite/i_main/t/gis.test
  Adding tests

@  sql/spatial.cc
  Returning on error if n_points value in the input WKB data
  exceeds max_n_points

@  sql/spatial.h
  Adding declarations for
  Gis_multi_point::max_n_points and Gis_line_string::max_n_points