open if statement in prelp.m

[mkarikom]

This appears to be a bug:

if ~exist('loadata','file') || ~exist('preprocess','file')
if ~exist('loadata','file') | ~exist('preprocess','file')
    error('To use PRELP, you need to have LIPSOL installed.')
end

removing the second if fixes compilation errors in mcc

[siko1056]

Confirmed. I found another duplicate which just does the work of loading data twice. Both are fixed with pr #48.