Added the ability to track the closure of the file manager without se…

…lecting content (kivy#667)

* Added the ability to track the closure of the file manager without selecting content
* extracting that duplicate logic to a helper method

plyer/platforms/linux/filechooser.py

@@ -64,13 +64,16 @@ def _run_command(self, cmd):
             if ret is not None:
                 if ret == self.successretcode:
                     out = self._process.communicate()[0].strip().decode('utf8')
-                    self.selection = self._split_output(out)
-                    self._handle_selection(self.selection)
-                    return self.selection
+                    return self._set_and_return_selection(self._split_output(out))
                 else:
-                    return None
+                    return self._set_and_return_selection(None)
             time.sleep(0.1)
 
+    def _set_and_return_selection(self, value):
+        self.selection = value
+        self._handle_selection(value)
+        return value
+
     def _split_output(self, out):
         '''This methods receives the output of the back-end and turns
         it into a list of paths.