fetch() hangs when mapping from char 0 to char p > 0

[steenpass]

The following simple example doesn't finish on my computer with a recent development version of Singular:

ring r = (0,a), (x,y,z), dp;
module m = (a)*x*gen(1)+536870909*y*gen(3);
ring s = (536870909,a), (x,y,z), dp;
module m = fetch(r, m);

[hannes]

fixed with 2a4231766997cb703074cd965636c35b364d526d (and prev.)