Problem: Debug builds fail an assertion when trying to do ALTER
TABLE on an ARCHIVE engine table with a GEOMETRY NOT NULL
column containing empty strings. Release builds return an error.

GEOMETRY columns should never hold empty strings as it is not
a valid geometric object. This is enforced by
Field_geom::store_internal(). However, in non-strict mode,
it is possible to trick the server into storing empty strings
in GEOMETRY NOT NULL columns by inserting NULL, which is then
converted to an empty string.

Later, when doing ALTER TABLE, these empty string values fail
an assertion in Field_geom::store_internal().

Fix: Remove the failing assertion, as such invalid values may
exist, and strengthen the check for too short geometry values
in Field_geom::store_internal(). Raise an error if trying to
insert a NULL value to a GEOMETRY NOT NULL column, regardless
of strict mode settings.

Note: This is the backport of Bug#85059
Change-Id: I8a0a5da8c46f2755d4bf6e0c6ab0fa3d7e2d5048