ART: Fast-fail empty other handlers in fault handling

Don't try to set up the nested handler environment if there are
no other handlers installed.

Stop-gap for the current setup without other handlers. There are
a myriad more issues before we can safely re-enable other handlers.

Bug: 28245957
Change-Id: I526aef82aa1ca2b6c4b1959858fe76231bc067d9
diff --git a/runtime/fault_handler.cc b/runtime/fault_handler.cc
index 5c5abeb..9f073a6 100644
--- a/runtime/fault_handler.cc
+++ b/runtime/fault_handler.cc
@@ -147,6 +147,10 @@
 }
 
 bool FaultManager::HandleFaultByOtherHandlers(int sig, siginfo_t* info, void* context) {
+  if (other_handlers_.empty()) {
+    return false;
+  }
+
   Thread* self = Thread::Current();
 
   DCHECK(self != nullptr);