Fix non-GUI usage in BOPTools

Only define the translation related functions if the GUI is up

src/Mod/Part/BOPTools/SplitFeatures.py

@@ -37,18 +37,18 @@
 #-------------------------- translation-related code ----------------------------------------
 #(see forum thread "A new Part tool is being born... JoinFeatures!"
 #http://forum.freecadweb.org/viewtopic.php?f=22&t=11112&start=30#p90239 )
-try:
-    _fromUtf8 = QtCore.QString.fromUtf8
-except Exception:
-    def _fromUtf8(s):
-        return s
-try:
-    _encoding = QtGui.QApplication.UnicodeUTF8
-    def _translate(context, text, disambig):
-        return QtGui.QApplication.translate(context, text, disambig, _encoding)
-except AttributeError:
-    def _translate(context, text, disambig):
-        return QtGui.QApplication.translate(context, text, disambig)
+    try:
+        _fromUtf8 = QtCore.QString.fromUtf8
+    except Exception:
+        def _fromUtf8(s):
+            return s
+    try:
+        _encoding = QtGui.QApplication.UnicodeUTF8
+        def _translate(context, text, disambig):
+            return QtGui.QApplication.translate(context, text, disambig, _encoding)
+    except AttributeError:
+        def _translate(context, text, disambig):
+            return QtGui.QApplication.translate(context, text, disambig)
 #--------------------------/translation-related code ----------------------------------------
 
 def getIconPath(icon_dot_svg):