Invalid type syntax for pair segfaults the compiler

[megane]

Compiling this kills the compiler (note the spurious dot):
(: foo (pair * . *))

Error: during expansion of (: ...) - segmentation violation

	Call history:

	<syntax>	  (##core#begin (: foo (pair * . *)))
	<syntax>	  (: foo (pair * . *))	<--

[sjamaan]

Thanks for finding this! It's a pretty serious problem, given that length will crash when passed an improper list.

[evhan]

Fixed by 075e5833 (master) and a8b11466 (chicken-5).