Disable mterp if unstarted runtime

Mterp uses entrypoints that assume the runtime is started.  If it isn't,
revert to the fallback interpreter.

Bug: 26510411

Change-Id: I08278981ee1e7bc21163c6584426cc18a5e261fc
diff --git a/runtime/interpreter/interpreter.cc b/runtime/interpreter/interpreter.cc
index 47e2e98..6b5218d 100644
--- a/runtime/interpreter/interpreter.cc
+++ b/runtime/interpreter/interpreter.cc
@@ -294,7 +294,7 @@
         const instrumentation::Instrumentation* const instrumentation =
             Runtime::Current()->GetInstrumentation();
         while (true) {
-          if (instrumentation->IsActive()) {
+          if (instrumentation->IsActive() || !Runtime::Current()->IsStarted()) {
             // TODO: allow JIT profiling instrumentation.  Now, just punt on all instrumentation.
 #if !defined(__clang__)
             return ExecuteGotoImpl<false, false>(self, code_item, shadow_frame, result_register);