ec.c: Don't lose error status when constructing points from a sequence.

ec.c: Don't lose error status when constructing points from a sequence.

The code would call `ecptxl_2' or `ecptxl_3' as appropriate, stash the
error status in `rc', and then fall out of the `if/else if' ladder to
`ok' -- which clobbers `rc', losing the error.  This is unfortunate if
the point has been partially filled in.

The right fix is to go unconditionally to `end'.  We already have `rc'
set appropriately, so `ok' isn't necessary; `ecptxl_2' has already
converted the point to internal form, and `ecptxl_3' constructs the
point in internal form anyway, so it would be wrong to drop into `fix'.