vm: Always fix top's line number when catching a raise. Fixes GH#12.

I did a small audit of show where I looked at various places and I couldn't
find anywhere that the line numbering was wrong.

The reason that I saw line 0 issues in aft was because anything that raises
an error in the vm without using a helper would cause the line number to not
be fixed. Errors from nomem are raised directly, thus causing the problem.