MDEV-4295 Server crashes in get_point on a query with Area, AsBinary, MultiPoint.

        Need to check if the number of points is 0 for the polygon.

mysql-test/r/gis.result

@@ -1108,4 +1108,10 @@ NULL
 SELECT Centroid( AsBinary( LineString(Point(0,0), Point(0,0), Point(0,0) )));
 Centroid( AsBinary( LineString(Point(0,0), Point(0,0), Point(0,0) )))
 NULL
+#
+# MDEV-4295 Server crashes in get_point on a query with Area, AsBinary, MultiPoint
+#
+SELECT Area(AsBinary(MultiPoint(Point(0,9), Point(0,1), Point(2,2))));
+Area(AsBinary(MultiPoint(Point(0,9), Point(0,1), Point(2,2))))
+NULL
 End of 5.1 tests

mysql-test/t/gis.test

@@ -839,4 +839,9 @@ select geometryn(0x0100000000070000000100000001030000000200000000000000ffffff0f,
 --echo #
 
 SELECT Centroid( AsBinary( LineString(Point(0,0), Point(0,0), Point(0,0) )));
+
+--echo #
+--echo # MDEV-4295 Server crashes in get_point on a query with Area, AsBinary, MultiPoint
+--echo #
+SELECT Area(AsBinary(MultiPoint(Point(0,9), Point(0,1), Point(2,2))));
 --echo End of 5.1 tests

sql/spatial.cc

@@ -868,7 +868,7 @@ int Gis_polygon::area(double *ar, const char **end_of_data) const
     if (no_data(data, 4))
       return 1;
     n_points= uint4korr(data);
-    if (n_points > max_n_points ||
+    if (n_points == 0 || n_points > max_n_points ||
         no_data(data, (SIZEOF_STORED_DOUBLE*2) * n_points))
       return 1;
     get_point(&prev_x, &prev_y, data+4);
@@ -989,7 +989,7 @@ int Gis_polygon::centroid_xy(double *x, double *y) const
       return 1;
     org_n_points= n_points= uint4korr(data);
     data+= 4;
-    if (n_points > max_n_points ||
+    if (n_points == 0 || n_points > max_n_points ||
         no_data(data, (SIZEOF_STORED_DOUBLE*2) * n_points))
       return 1;
     get_point(&prev_x, &prev_y, data);