Ensure isolate exists in ReportApiFailure

This avoids a segfault rather than reporting the (API usage)
error message:
"Fatal error in v8::HandleScope::CreateHandle() Cannot create a
handle without a HandleScope"


Bug: 
Cq-Include-Trybots: master.tryserver.chromium.linux:linux_chromium_rel_ng
Change-Id: I68a3d77ca37cc09d9e70526008a072dee8973000
Reviewed-on: https://chromium-review.googlesource.com/832488
Commit-Queue: Wael Al Jishi <waelj@google.com>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50485}

src/api.cc

@@ -402,7 +402,10 @@ void i::V8::FatalProcessOutOfMemory(const char* location, bool is_heap_oom) {
 
 void Utils::ReportApiFailure(const char* location, const char* message) {
   i::Isolate* isolate = i::Isolate::Current();
-  FatalErrorCallback callback = isolate->exception_behavior();
+  FatalErrorCallback callback = nullptr;
+  if (isolate != nullptr) {
+    callback = isolate->exception_behavior();
+  }
   if (callback == nullptr) {
     base::OS::PrintError("\n#\n# Fatal error in %s\n# %s\n#\n\n", location,
                          message);