wspr: Fix an issue where we deadlock on shutdown because we are blocked
on caveat validation.

The prefix fix was not sufficient, since it didn't handle the case where
the request was sent to JS before the tab was closed.

Change-Id: Ie5961086b52167781f33eb3ec879c9a6e676ec97
diff --git a/services/wspr/internal/rpc/server/server.go b/services/wspr/internal/rpc/server/server.go
index 02e05e7..a30a728 100644
--- a/services/wspr/internal/rpc/server/server.go
+++ b/services/wspr/internal/rpc/server/server.go
@@ -393,6 +393,8 @@
 	}
 
 	select {
+	case <-s.statusClose:
+		return caveatValidationInGo(ctx, call, cavs)
 	case <-timeoutChan:
 		return makeListOfErrors(len(cavs), NewErrCaveatValidationTimeout(ctx))
 	case reply := <-replyChan: