Fixed, Draw Grid mode: fixed a crash on accepting the mode when start and end...

Fixed, Draw Grid mode: fixed a crash on accepting the mode when start and end points had the same coordinates.
Fixed, Draw Grid mode: grid triangles are now aligned properly with previously drawn triangulated grids when using the same map grid size and "Lock slices to grid" and "Triangulate" options are enabled.
Fixed, Draw Grid mode: not all grid cells were drawn in some cases.
Fixed, Draw Grid mode: current grid size was not increased when "Lock slices to grid" was enabled and the start point was no longer on the map grid.
Changed, Draw Grid mode: snap to grid is now always enabled and snap to nearest is now always disabled when "Lock slices to grid" is enabled.
Changed, Draw Grid mode: when grid's width or height is 0 when accepting the mode, a segmented line is now drawn instead of just a line.