Do a null check on the OatQuickMethodHeader.

Even if we found a method at the bottom of the stack, we may be
executing something unrelated to it. That's when GetOatQuickMethodHeader
will return null. So do a null check and return if we did not find any
compiled code.

Test: build
Bug: 173753901
Change-Id: I05595d601e0523b1254581c306b157b273828c53
diff --git a/runtime/fault_handler.cc b/runtime/fault_handler.cc
index cae7deb..51ac2c3 100644
--- a/runtime/fault_handler.cc
+++ b/runtime/fault_handler.cc
@@ -329,6 +329,11 @@
 
   const OatQuickMethodHeader* method_header = method_obj->GetOatQuickMethodHeader(return_pc);
 
+  if (method_header == nullptr) {
+    VLOG(signals) << "no compiled code";
+    return false;
+  }
+
   // We can be certain that this is a method now.  Check if we have a GC map
   // at the return PC address.
   if (true || kIsDebugBuild) {