Fix for issue 24487951 (heap buffer overflow problem)

runtime/bin/dartutils.cc

Index: runtime/bin/dartutils.cc
diff --git a/runtime/bin/dartutils.cc b/runtime/bin/dartutils.cc
index a4fc2e2f671117ec2c67178ec70e0c53f2d9fd45..83ffcd35f994e5b5ed2c8a97908e91a960927c50 100644
--- a/runtime/bin/dartutils.cc
+++ b/runtime/bin/dartutils.cc
@@ -464,6 +464,10 @@ const uint8_t* DartUtils::SniffForMagicNumber(const uint8_t* text_buffer,
                                               intptr_t* buffer_len,
                                               bool* is_snapshot) {
   intptr_t len = sizeof(magic_number);
+  if (*buffer_len <= len) {
+    *is_snapshot = false;
+    return text_buffer;
+  }
   for (intptr_t i = 0; i < len; i++) {
     if (text_buffer[i] != magic_number[i]) {
       *is_snapshot = false;