lang: Don't race with a ^C to the obj.lang calls

If we trigger a close, we must not run the LangClose before we've exited
from the loop, because that loop could race and run code which depends
on LangClose not having run first. So run the loop shutdown, then let
the wait group expire, before shutting down the lang.

lang/gapi.go

@@ -178,7 +178,10 @@ func (obj *GAPI) Next() chan gapi.Next {
 				Err:  fmt.Errorf("%s: GAPI is not initialized", Name),
 				Exit: true, // exit, b/c programming error?
 			}
-			ch <- next
+			select {
+			case ch <- next:
+			case <-obj.closeChan:
+			}
 			return
 		}
 		startChan := make(chan struct{}) // start signal
@@ -259,9 +262,9 @@ func (obj *GAPI) Close() error {
 	if !obj.initialized {
 		return fmt.Errorf("%s: GAPI is not initialized", Name)
 	}
-	obj.LangClose() // close lang, esp. if blocked in Stream() wait
 	close(obj.closeChan)
 	obj.wg.Wait()
+	obj.LangClose()         // close lang, esp. if blocked in Stream() wait
 	obj.initialized = false // closed = true
 	return nil
 }