Minor code cleanup

Patch by Terry Wilmarth

Differential Revision: https://reviews.llvm.org/D41831

llvm-svn: 322203
diff --git a/openmp/runtime/src/kmp_tasking.cpp b/openmp/runtime/src/kmp_tasking.cpp
index 97baaf7..0eac113 100644
--- a/openmp/runtime/src/kmp_tasking.cpp
+++ b/openmp/runtime/src/kmp_tasking.cpp
@@ -984,9 +984,10 @@
 // thread:  thread data structure corresponding to implicit task
 void __kmp_free_implicit_task(kmp_info_t *thread) {
   kmp_taskdata_t *task = thread->th.th_current_task;
-  if (task->td_dephash)
+  if (task && task->td_dephash) {
     __kmp_dephash_free(thread, task->td_dephash);
-  task->td_dephash = NULL;
+    task->td_dephash = NULL;
+  }
 }
 
 // Round up a size to a power of two specified by val: Used to insert padding