Path: Fix update of Extensions Default Length GUI spin box

Fix the bug hindering update of the Default Length spin box in the Extensions tab after editing and change of focus. 
With the fix, the spin box updates after change of focus, as do other spin boxes in the Path workbench.
Used method found in PathDrillingGui module.

src/Mod/Path/PathScripts/PathPocketShapeGui.py

@@ -222,7 +222,7 @@ class TaskPanelExtensionPage(PathOpGui.TaskPanelPage):
 
         if obj.ExtensionCorners != self.form.extendCorners.isChecked():
             self.form.extendCorners.toggle()
-        self.defaultLength.updateSpinBox()
+        self.updateQuantitySpinBoxes()
         self.extensions = obj.Proxy.getExtensions(obj) # pylint: disable=attribute-defined-outside-init
         self.setExtensions(self.extensions)
 
@@ -341,11 +341,15 @@ class TaskPanelExtensionPage(PathOpGui.TaskPanelPage):
 
         self.form.extensionTree.blockSignals(False)
 
+    def updateQuantitySpinBoxes(self, index = None):
+        self.defaultLength.updateSpinBox()
+
     def updateData(self, obj, prop):
         PathLog.track(obj.Label, prop, self.blockUpdateData)
         if not self.blockUpdateData:
             if prop in ['Base', 'ExtensionLengthDefault']:
                 self.setExtensions(obj.Proxy.getExtensions(obj))
+                self.updateQuantitySpinBoxes()
 
     def restoreSelection(self, selection):
         PathLog.track()
@@ -458,6 +462,7 @@ class TaskPanelExtensionPage(PathOpGui.TaskPanelPage):
         self.form.buttonClear.clicked.connect(self.extensionsClear)
         self.form.buttonDisable.clicked.connect(self.extensionsDisable)
         self.form.buttonEnable.clicked.connect(self.extensionsEnable)
+        self.form.defaultLength.editingFinished.connect(self.updateQuantitySpinBoxes)
 
         self.model.itemChanged.connect(self.updateItemEnabled)