[shotwell] Fix "Unknown source id" warnings

[Jens Georg <jensgeorg src gnome org>]

commit 848b55972ef8d35e272a4354ad2446dd80354dd0
Author: Jens Georg <mail jensge org>
Date:   Fri Oct 12 10:35:26 2018 +0200

    Fix "Unknown source id" warnings

 src/Page.vala | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)
---
diff --git a/src/Page.vala b/src/Page.vala
index b92eaa0c..ea76ac15 100644
--- a/src/Page.vala
+++ b/src/Page.vala
@@ -1115,15 +1115,19 @@ public abstract class Page : Gtk.ScrolledWindow {
     }
 
     public void stop_cursor_hiding() {
-        if (last_timeout_id != 0)
+        if (last_timeout_id != 0) {
             Source.remove(last_timeout_id);
+            last_timeout_id = 0;
+        }
     }
 
     public void suspend_cursor_hiding() {
         cursor_hide_time_cached = cursor_hide_msec;
 
-        if (last_timeout_id != 0)
+        if (last_timeout_id != 0) {
             Source.remove(last_timeout_id);
+            last_timeout_id = 0;
+        }
 
         cursor_hide_msec = 0;
     }