[OMPT] Fix assertion in per-device-enabled tracing (#362)

OpenMP allows to disable trace events on a per-device basis.
#340 at the latest introduced a
bug which does not respect the disabling of specific trace events.

This fix adds checks whether the required data has been set when
creating the OMPT info before dispatching the actual operation on the
plugins.

Author: jplehr

offload/plugins-nextgen/common/OMPT/OmptProfiler.cpp

@@ -93,6 +93,11 @@ void llvm::omp::target::ompt::OmptProfilerTy::handleKernelCompletion(
   if (!isProfilingEnabled())
     return;
 
+  /// Empty data means no tracing in OMPT
+  /// offload/include/OpenMP/OMPT/Interface.h line 492
+  if (!Data)
+    return;
+
   DP("OMPT-Async: Time kernel for asynchronous execution (Plugin): Start %lu "
      "End %lu\n",
      StartNanos, EndNanos);
@@ -115,6 +120,11 @@ void llvm::omp::target::ompt::OmptProfilerTy::handleDataTransfer(
   if (!isProfilingEnabled())
     return;
 
+  /// Empty data means no tracing in OMPT
+  /// offload/include/OpenMP/OMPT/Interface.h line 492
+  if (!Data)
+    return;
+
   auto OmptEventInfo = reinterpret_cast<ompt::OmptEventInfoTy *>(Data);
   assert(OmptEventInfo && "Invalid OmptEventInfo");
   assert(OmptEventInfo->TraceRecord && "Invalid TraceRecord");