fix misleading FATAL EXCEPTION IN SYSTEM PROCESS log

There will be the following situations about mApplicationObject：

1) fork app process will invoke ActivityThread.main(),
then set mApplicationObject.

2) fork system_server， don't set mApplicationObject value.

3) using app_process fork process except zygote, will inovke RuntimeInit,
don't set mApplicationObject value。

For example using command as below:
app_process /system/bin com.android.commands.am.Am "$@",

if this process throw uncaught exception，will output FATAL EXCEPTION IN SYSTEM PROCESS log，
it's not in system process but in normal process。

so should add condition： Process.SYSTEM_UID == Process.myUid()

BUG: 72759350
Test: manual

Change-Id: Ie8d769e4149cd9b938577058de871c4f8db9efe5
Signed-off-by: yuanhuihui <yuanhuihui@xiaomi.com>