mat v4 compat: read namelen with given length and strip trailing null

[songjhaha]

we have some old mat file，but the name is store without null-terminator '\0'(it could be create from some old c program).

MATLAB and scipy is compat with these file.

here is a test .m script to generate example mat file:

fid = fopen('testnamelen_4.2c_SOL2.mat', 'wb')
data = rand(1,9);
[M, N] = size(data);
data_type = 0;
prec = 'double';
name = 'testnamelen';

L = length(name);

fwrite(fid, data_type, 'int32');

fwrite(fid, M, 'int32');

fwrite(fid, N, 'int32');
fwrite(fid, 0, 'int32');
fwrite(fid, L, 'int32');
fwrite(fid, name, 'uint8');
fwrite(fid, data, prec);

data1 = load('testnamelen_4.2c_SOL2.mat');

assert(all(data1.(name)==data))

[songjhaha]

@ViralBShah could you review this PR?