Fix for few similar bugs:

  #841622 Assertion `t->rp->type == Gcalc_function::shape_line' failed in Gcalc_operation_reducer::end_line in maria-5.3-gi
  #841625 Assertion `m_poly_borders->next' failed in Gcalc_operation_reducer::count_slice in maria-5.3-gis
  #841638 Assertion `!m_prev || m_prev->x != x || m_prev->y != y' failed in Gcalc_shape_transporter::int_add_point in maria-5.3-gis
  #841662 Third assertion `n > 0 && n < SINUSES_CALCULATED*2+1' in get_n_sincos
  #841745 Assertion `!sp0->is_bottom()' failed in Gcalc_scan_iterator::find_intersections in maria-5.3-gis

  They mostly was caused by inprecision of double arithmetic.
  Fixed by changes in how to handle multiple intersections to keep their order right.

  Also ST_DISTANCE(GEOM, EMPTY_GEOM) was defined as NULL.


per-file comments:
  mysql-test/r/gis-precise.result
   GIS bugfixes.
        test result updated.
  mysql-test/t/gis-precise.test
   GIS bugfixes.
        test cases added.
  sql/gcalc_slicescan.cc
   GIS bugfixes.
        If intersections are close, add order checks to cope with the
        double calcualtions imprecision.
  sql/gcalc_slicescan.h
   GIS bugfixes.
        n_row parameter added to intersection to check their order.
  sql/item_geofunc.cc
   GIS bugfixes.
        ST_DISTANCE(GEOM, EMPTY_GEOM) returns NULL.

1 files changed, 8 insertions, 0 deletions

diff --git a/sql/item_geofunc.cc b/sql/item_geofunc.cc
index ea849bb10a3..631b63812b5 100644
--- a/sql/item_geofunc.cc
+++ b/sql/item_geofunc.cc
@@ -1789,6 +1789,14 @@ double Item_func_distance::val_real()
   if (g2->store_shapes(&trn) || func.alloc_states())
     goto mem_error;
 
+  if (obj2_si == 0 || func.get_nshapes() == obj2_si)
+  {
+    distance= 0.0;
+    null_value= 1;
+    goto exit;
+  }
+
+
   collector.prepare_operation();
   scan_it.init(&collector);