check_matlab_path.m fails if there are files with single letter file names

Line 131 is as follows:

if isequal(dd(f).name(end-1:end),'.m')

If the file name is length 1, then end-1 evaluates to a 0, causing an error. A fix is included in this commit: https://github.com/tholden/dynare/commit/99742309d2fe3468bcdc7074a0120be00222912b in which that line is changed to:

if strcmpi(dd(f).name(max(1,end-1):end),'.m')