[pitivi] widgets: Fix methods that block/unblock signals of NumericWidget

[Alexandru Băluț <alexbalut src gnome org>]

commit dbc2ea39e0d30fdcde721b4bd455a63e08c25cbf
Author: Suhas Nayak <suhas2go gmail com>
Date:   Mon Sep 25 01:04:18 2017 +0530

    widgets: Fix methods that block/unblock signals of NumericWidget
    
    If an adjustment has not been connected yet, then the handler_id
    is None. handler_block/unblock shouldn't be called in such cases.
    
    Differential Revision: https://phabricator.freedesktop.org/D1865

 pitivi/utils/widgets.py |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/pitivi/utils/widgets.py b/pitivi/utils/widgets.py
index 039006f..2f84888 100644
--- a/pitivi/utils/widgets.py
+++ b/pitivi/utils/widgets.py
@@ -266,10 +266,12 @@ class NumericWidget(Gtk.Box, DynamicWidget):
         disable_scroll(self.spinner)
 
     def block_signals(self):
-        self.adjustment.handler_block(self.handler_id)
+        if self.handler_id:
+            self.adjustment.handler_block(self.handler_id)
 
     def unblock_signals(self):
-        self.adjustment.handler_unblock(self.handler_id)
+        if self.handler_id:
+            self.adjustment.handler_unblock(self.handler_id)
 
     def connectValueChanged(self, callback, *args):
         self.handler_id = self.adjustment.connect("value-changed", callback, *args)