Update the currentCalls before VTS notification.

It's reasonable to update the global variable "currentCalls" before
notifying the reader thread. Otherwise this can cause some issues such
as null pointer dereference in other modem.

Bug: 139264227
Test: Don't have devices that uses the corresponding modem that reports
 this issues. This is verified according to a partner CL:
https://partner-android-review.googlesource.com/c/platform/hardware/interfaces/+/1422356

Change-Id: Iee9e18149397c39b7c84ec1dc570b9bac7142eb6