3958 – mixin(non-static method) crashes compiler

struct S
{
	string g() { return ""; }
	void f() { mixin(g()); }
}
Making g() static stops DMD from crashing.

There's another problem. This fails to compile:
struct S
{
 static string g() { return null; }
 void f() { mixin(g()); } //line 4
}
z.d(4): Error: argument to mixin must be a string, not (null)
(Tested with dmd v2.041.)

PATCH(against 2.042): This is trivial.
// interpret.c line 2569:
 if (pthis && fd)
 { // Member function call
	if (pthis->op == TOKthis)
-	 pthis = istate->localThis;
+	 pthis = istate ? istate->localThis : NULL;
	else if (pthis->op == TOKcomma)
	 pthis = pthis->interpret(istate);
The second issue is that mixin(null); is never allowed. It's completely unrelated to this bug. Create a new bug for it if you think it matters.

changeset 424

Fixed DMD1.048 and 2.043.