Fix for issue 27094147 (Null pointer deref in IsScriptSnapshot).

runtime/vm/dart_api_impl.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "include/dart_api.h"
 #include "include/dart_mirrors_api.h"
 #include "include/dart_native_api.h"
 
 #include "platform/assert.h"
 #include "lib/stacktrace.h"
@@ skipping 5113 matching lines @@
   API_TIMELINE_DURATION;
   DARTSCOPE(Thread::Current());
   Isolate* I = T->isolate();
   StackZone zone(T);
   if (buffer == NULL) {
     RETURN_NULL_ERROR(buffer);
   }
   NoHeapGrowthControlScope no_growth_control;
 
   const Snapshot* snapshot = Snapshot::SetupFromBuffer(buffer);
+  if (snapshot == NULL) {
+    return Api::NewError("%s expects parameter 'buffer' to be a script type"
+                         " snapshot with a valid length.", CURRENT_FUNC);
+  }
   if (!snapshot->IsScriptSnapshot()) {
     return Api::NewError("%s expects parameter 'buffer' to be a script type"
                          " snapshot.", CURRENT_FUNC);
   }
   if (snapshot->length() != buffer_len) {
     return Api::NewError("%s: 'buffer_len' of %" Pd " is not equal to %" Pd
                          " which is the expected length in the snapshot.",
                          CURRENT_FUNC, buffer_len, snapshot->length());
   }
   Library& library = Library::Handle(Z, I->object_store()->root_library());
@@ skipping 1013 matching lines @@
   return Api::Success();
 }
 #endif  // DART_PRECOMPILER
 
 
 DART_EXPORT bool Dart_IsRunningPrecompiledCode() {
   return Dart::IsRunningPrecompiledCode();
 }
 
 }  // namespace dart