Viewport: draw floor routine should not use GL_ALWAYS for depth

(talked with merwin about that, and he agrees on it, we are not supposed to write to the scene depth buffer
but we should read its depth)

source/blender/editors/space_view3d/view3d_draw.c

@@ -609,8 +609,6 @@ static void drawfloor(Scene *scene, View3D *v3d, const char **grid_unit, bool wr
 
 			immBindBuiltinProgram(GPU_SHADER_3D_FLAT_COLOR);
 
-			glDepthFunc(GL_ALWAYS); /* draw lines in order given */
-
 			immBegin(GL_LINES, vertex_ct);
 
 			/* draw normal grid lines */
@@ -687,8 +685,6 @@ static void drawfloor(Scene *scene, View3D *v3d, const char **grid_unit, bool wr
 			immUnbindProgram();
 
 			/* done with XY plane */
-
-			glDepthFunc(GL_LESS); /* restore default */
 		}
 
 		if (show_axis_x || show_axis_y || show_axis_z) {