Use default value when unpacking variable vector.

* geesh/environment.scm (getvar): Use 'dflt' when we have a vector but
'value' is '#f'.

geesh/environment.scm

@@ -151,7 +151,7 @@ well."
 and @var{dflt} is provided, return @var{dflt}.  Otherwise, return
 @code{#f}."
   (match (hash-ref *variables* name dflt)
-    (#(value _ _) value)
+    (#(value _ _) (or value dflt))
     (value value)))
 
 (define (setvar! name value)