Add initialization of c1 to sylvester3.m

Prevents crashes in older Matlab versions for pathological cases (e.g. if p=0)

matlab/gensylv/sylvester3.m

@@ -52,6 +52,7 @@ else
 end
 i = 1;
 c = zeros(n,1,p);
+c1 = zeros(n,1,p);
 while i < m
     if t(i+1,i) == 0
         if i == 1