How to exit a for loop whenever we can't find XX consecutive non-zero values??Momentum Portfolio Construction

 Hi everyone. I am trying to construct momentum portfolios but I encounter some missing values problem.
I converted all missing values into 0 and I calculate the number of eligible values (non-missing) in every row in the first loop.

Then I calculate the six month returns of every stock just by adding the simple returns over 6 months.

The problem comes when there's a missing values (which is '0') let's say at month '3'. With my loop number 2 I add these zero as zero return months, when they were missing values.

What I would like to do is to exit the loop whenever there's a 0 in the first or in the following 5 months. Whenever there are not 6 non-zero consecutive values, matlab should return me with empty cases.

Let's say if there's a 0 on the 4th month, it should return empty case till month n4 and then restart looping from month number 5.

Any help? Thank you veeeery much

for i=1:totalmonths

sum0=sum(stockdata(i,:)==0);

sumstockdata(i,:)=sum0;

 nbrstocks(i) = totalstocks - sumstockdata(i); 

 end

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% for j=1:1026

 for i=1:487

   k=i+5;

 somma(i,j) = sum(stockdata((i:k),j));

 end
end

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

for j=1:1026

 for i=1:487

   k=i+5;

   if stockdata(i,j)==0

      somma2(i,j)=0;
   else

        somma2(i,j) = sum(stockdata((i:k),j));
 end
 end
end