CMFileManager: Fix crash when select CMFileManager internal editor to open text file.

    When open a text file, in the choose application to open and select
the CMFileManager internal editor to open, the CMFileManager will crash.
Because the ri.filter is null.

    Patch Set 2:
        Implement the logical as Jorge Ruesga suggestion. Check it's interneal editor
    before to process system association.

    Patch Set 3:
        Add the ri.filter valid check before to process system association.

Change-Id: I2d9698d9cb862de2b1141e84bc2f540e4ced92e6