[tracker] tracker-store: Check wal threadpool existence before using it

[Carlos Garnacho <carlosg src gnome org>]

commit 2b0ad4b297c0d7dc31296fb1dadae3b092e9898b
Author: Carlos Garnacho <carlosg gnome org>
Date:   Sun Jul 16 19:53:13 2017 +0200

    tracker-store: Check wal threadpool existence before using it
    
    During shutdown the thread pool might be actually gone. Do not try to poke
    it in those situations, a blocking wal checkpoint will happen eventually.

 src/tracker-store/tracker-store.vala |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/src/tracker-store/tracker-store.vala b/src/tracker-store/tracker-store.vala
index 801a539..1f58256 100644
--- a/src/tracker-store/tracker-store.vala
+++ b/src/tracker-store/tracker-store.vala
@@ -274,7 +274,7 @@ public class Tracker.Store {
                        // do immediate checkpointing (blocking updates)
                        // to prevent excessive wal file growth
                        wal_checkpoint (wal_iface, true);
-               } else if (n_pages >= 1000) {
+               } else if (n_pages >= 1000 && checkpoint_pool != null) {
                        if (AtomicInt.compare_and_exchange (ref checkpointing, 0, 1)) {
                                // initiate asynchronous checkpointing (not blocking updates)
                                try {