Don't post debug exceptions if debugger not active.

Change-Id: I67f0b62945f9d17ca62d45492331e55c72196631
diff --git a/src/debugger.cc b/src/debugger.cc
index dea4339..df55f4e 100644
--- a/src/debugger.cc
+++ b/src/debugger.cc
@@ -1433,6 +1433,9 @@
 }
 
 void Dbg::PostException(Method** sp, Method* throwMethod, uintptr_t throwNativePc, Method* catchMethod, uintptr_t catchNativePc, Object* exception) {
+  if (!gDebuggerActive) {
+    return;
+  }
   JDWP::JdwpLocation throw_location;
   SetLocation(throw_location, throwMethod, throwNativePc);
   JDWP::JdwpLocation catch_location;