Fix 26132: UBL probe_entire_mesh could skip points

[mriscoc]

UBL probe_entire_mesh could skip points at the end of the mesh loop if invalid points are found.

G29 P1 normally invalidates the mesh by filling it with NAN previously to call probe_entire_mesh.

The function probe_entire_mesh loads the total number of mesh points in the count variable.

Marlin/Marlin/src/feature/bedlevel/ubl/ubl_G29.cpp

Line 765 in 347a7dc

grid_count_t count = GRID_MAX_POINTS;

And to get the next point to probe uses the following:

Marlin/Marlin/src/feature/bedlevel/ubl/ubl_G29.cpp

Lines 789 to 791 in 347a7dc

	best = do_furthest
	? find_furthest_invalid_mesh_point()
	: find_closest_mesh_point_of_type(INVALID, nearby, true);

Both functions (find_furthest_invalid_mesh_point and find_closest_mesh_point_of_type) use NAN as a flag to find out points to be probed and skip points with valid values.

But if there is a failure in probe.probe_at_point the current point is filled with NAN, so find_furthest_invalid_mesh_point or find_closest_mesh_point_of_type will try to probe that same point again.

That will continue until the main loop ends mainly because the variable count is decreased to 0.

Requirements

UBL enabled

Benefits

An invalid mesh point must be flagged and skipped to allow probe_entire_mesh to continue to the next point.

Related Issues

This PR solves: #26132