Fix misleading message when processing empty directories

kcc/KCC_gui.py

@@ -136,6 +136,10 @@ class WorkerThread(QtCore.QThread):
             try:
                 outputPath = comic2ebook.main(jobargv, self)
                 self.emit(QtCore.SIGNAL("hideProgressBar"))
+            except UserWarning as warn:
+                self.errors = True
+                self.emit(QtCore.SIGNAL("addMessage"), 'KCC failed to create output file!', 'warning')
+                self.emit(QtCore.SIGNAL("addMessage"), str(warn), 'warning')
             except Exception as err:
                 self.errors = True
                 type_, value_, traceback_ = sys.exc_info()