Strange DMD Assertion failure

[Chris Miller]

Compiling code that worked fine with DMD 0.160 now fails on DMD 0.161 with  
the following compiler error:
    Assertion failure: 'next' on line 2226 in file 'mtype.c'

Looking at mtype.c I notice the assert makes sure 'next' is not null, but  
on the next line it checks 'next' for null and acts appropriately; also,  
in the same function of DMD 0.160 this null check is not there, only the  
assert, so it leads me to believe that perhaps the new compiler now allows  
a null 'next' but the assert was left accidentally.

I tried simplifying my code to make a small reproducable example, but this  
project is huge and the changes were causing template mixin forward  
reference errors. Compiling with -v shows it fails on the first semantic  
pass.

- Chris