Fixed a crasher when handling process events that is due to a translation from the public API to the private API.

llvm-svn: 200267
diff --git a/lldb/source/Core/Debugger.cpp b/lldb/source/Core/Debugger.cpp
index 867e1de..dc7d30b 100644
--- a/lldb/source/Core/Debugger.cpp
+++ b/lldb/source/Core/Debugger.cpp
@@ -2871,7 +2871,8 @@
                         StopReason curr_thread_stop_reason = eStopReasonInvalid;
                         if (curr_thread)
                             curr_thread_stop_reason = curr_thread->GetStopReason();
-                        if (!curr_thread->IsValid() ||
+                        if (!curr_thread ||
+                            !curr_thread->IsValid() ||
                             curr_thread_stop_reason == eStopReasonInvalid ||
                             curr_thread_stop_reason == eStopReasonNone)
                         {