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

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
diff --git a/runtime/vm/dart_api_impl.cc b/runtime/vm/dart_api_impl.cc
index a826afe32ec274256420d2f23da88d6dc6738955..5e9b9cea7e2fcbfcb3fa92411488c68a332fd9ce 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -5131,6 +5131,10 @@ DART_EXPORT Dart_Handle Dart_LoadScriptFromSnapshot(const uint8_t* 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);