MAP: Fix possible NullPointerException while GetMessagesListing

Fix possible NullPointerException while processing GetMessagesListing
on a MSE without a valid SIM , case wherein invalid  messageType value
occurs on MAP SMS/MMS Instance. Now by default SMS type is set to GSM.

Following basic PTS test cases and also other PTS cases dependent on
GetMessagesListing functionality fail without this fix:
TC_MSE_MMB_BV_11_I
TC_MSE_MMB_BV_20_I
TC_MSE_MMU_BV_02_I

Change-Id: I8ed0a2787534159342af88ec413a1c0407961d91