Check if mSurface is valid before create SurfaceSession

If mSurface has already been released in another thread,
this would result in a null-pointer dereference in
SurfaceSession contructor i.e. in nativeCreateScoped().

7757  7757 F DEBUG   : pid: 1402, tid: 1583, name: android.anim  >>> system_server <<<
7757  7757 F DEBUG   : signal 11 (SIGSEGV), code 1 (SEGV_MAPERR), fault addr 0xd0
7757  7757 F DEBUG   : Cause: null pointer dereference
... <trimmed>
7757  7757 F DEBUG   : backtrace:
7757  7757 F DEBUG   :     #00 pc 000000000007fe58  /system/lib64/libgui.so (android::Surface::getIGraphicBufferProducer() const)
7757  7757 F DEBUG   :     #01 pc 00000000000ff000  /system/lib64/libandroid_runtime.so (android::nativeCreateScoped(_JNIEnv*, _jclass*, long)+52)
7757  7757 F DEBUG   :     #02 pc 0000000000ac8968  /system/framework/arm64/boot-framework.oat (offset 0x614000) (android.content.res.XmlBlock.nativeCreateParseState [DEDUPED]+152)
7757  7757 F DEBUG   :     #03 pc 0000000001327d24  /system/framework/arm64/boot-framework.oat (offset 0x614000) (android.view.SurfaceSession.<init>+52)
7757  7757 F DEBUG   :     #04 pc 00000000014b7320  /system/framework/oat/arm64/services.odex (offset 0x5be000) (com.android.server.wm.TaskSnapshotSurface.drawSizeMismatchSnapshot+128)
7757  7757 F DEBUG   :     #05 pc 00000000014b784c  /system/framework/oat/arm64/services.odex (offset 0x5be000) (com.android.server.wm.TaskSnapshotSurface.drawSnapshot+188)
7757  7757 F DEBUG   :     #06 pc 00000000014b6f2c  /system/framework/oat/arm64/services.odex (offset 0x5be000) (com.android.server.wm.TaskSnapshotSurface.create+2684)
7757  7757 F DEBUG   :     #07 pc 00000000014b0158  /system/framework/oat/arm64/services.odex (offset 0x5be000) (com.android.server.wm.TaskSnapshotController.createStartingSurface+72)
7757  7757 F DEBUG   :     #08 pc 00000000014a5ca0  /system/framework/oat/arm64/services.odex (offset 0x5be000) (com.android.server.wm.SnapshotStartingData.createStartingSurface+96)
7757  7757 F DEBUG   :     #09 pc 000000000144b030  /system/framework/oat/arm64/services.odex (offset 0x5be000) (com.android.server.wm.AppWindowContainerController.lambda$-com_android_server_wm_AppWindowContainerController_4735+496)
... <trimmed>

Bug: 74129970

Change-Id: I41268c7680d3885c85fc3b682d0eba7415674062