[CALL] Fixed frozen hangup when HANGUP request directly after ipc_call_end_callback
GET_CURRENT_CALL is not completed yet

Exmple:
I/RIL-Mocha-TAPI-PACKET(  154): Tapi call/general packet received
I/RIL-Mocha-TAPI-CALL(  154): tapi_call_parser - tapiCallType: 24
I/RIL-Mocha-IPC-LIB(  154): Invoking RIL callback of type 8
E/RIL-Mocha-CALL(  154): ipc_call_end: Test me!
I/RIL-Mocha-CALL(  154): ipc_call_end : callId = 3, cause = 24
D/RIL-Mocha-UTIL(  154): [0000]   03 00 00 00 18 00 00 00                             ........
D/RILJ    (  610): [UNSL]< UNSOL_RESPONSE_CALL_STATE_CHANGED
I/RIL-Mocha-IPC-PARSER(  154): Packet type 0x9a not yet handled
I/RIL-Mocha-IPC-PARSER(  154): Frame header = 0xcafecafe
I/RIL-Mocha-IPC-PARSER(  154):  Frame type = 0x9a
I/RIL-Mocha-IPC-PARSER(  154):  Frame length = 0x8
D/RIL-Mocha-IPC(  154): ipc: [0000] 04 86 68 00 B4 26 E4 00                            ..h.....
D/GSM     (  610): [GsmCallTracker] (ringing) hangup waiting or background
D/RILJ    (  610): [0341]> HANGUP_WAITING_OR_BACKGROUND
D/PHONE   (  610): Event EVENT_CALL_RING_CONTINUE Received stat=RINGING
D/PHONE   (  610): Sending notifyIncomingRing

Change-Id: Ibd36f8a41e21623d8bdb2cb1b5ed208c14e1f8f1