Fix empty array edge cases in nlinfit - #485

Matches MATLAB, which errors in all these cases. Remove the %!test block that holds only a comment (it always passes), give the %!error tests the full message with the nlinfit: prefix, and start the message after the prefix in lower case, e.g. "nlinfit: MODELFUN must return a vector of the same size as Y."

updated @pr0m1th3as
can you review again, thank you.

Please remove the rows (X) != rows (y) check. X is only passed to MODELFUN, so it can be anything the model function accepts; on main both of these fit, and with this change both error:

y = [2.1; 3.9; 6.2; 7.8; 10.1];
nlinfit ([], y, @(b, x) b(1) * (1:5)', 1)
nlinfit ({1:5}, y, @(b, x) b(1) * x{1}(:), 1)

MATLAB has no such check either; the size check on the output of MODELFUN is enough. Argument names keep their case (lower case is only for an ordinary first word after the prefix): nlinfit: MODELFUN must return a vector of the same size as Y. Update the %!error tests to the full messages and write zeros (0, 3) with spaces.

updated @pr0m1th3as

nlinfit ((1:6), (1:6), @(b, x) b(1) * x, 1) error with your PR, whereas it passes on main. Stop feeding my replies to an LLM-backed coding assistant and keep committing code that you haven't tested/checked properly.

fixing it, behaviour changed when i modified the if condition

can you review now @pr0m1th3as thank you.

Thanks for your reviews, @pr0m1th3as .