Fix system server crash during sendMyPackageSuspendedOrUnsuspended()

IllegalArgumentException could be thrown when the package doesn't exist
from getSuspendedPackageAppExtrasInternal(), which causes system server
crash

This fix replaces throwing IllegalStateException with returning null,
instead of handling the exception. Returning null when the package
doesn't exist still operates according to the public contact since
an uninstalled application would not be considered 'suspended'.

Bug: 171906179
Test: compile & verify basic functions working
Change-Id: I9b23c17530393a0f51e283d0bc2c44966ddf6298