ART: Address comment in Idaca9fe129ddc91aab79c65b3d0ca86f057848de

Address a late comment.

Test: m test-art-host
Change-Id: I34583fcafb3158609d1d126689aa7710c5dd693f
diff --git a/oatdump/oatdump_test.h b/oatdump/oatdump_test.h
index 18b8439..2c28f06 100644
--- a/oatdump/oatdump_test.h
+++ b/oatdump/oatdump_test.h
@@ -225,8 +225,7 @@
       if (len > 0) {
         size_t pos = error_buf.size();
         if (pos < MB) {
-          error_buf.resize(pos + len);
-          memcpy(error_buf.data() + pos, buf, len);
+          error_buf.insert(error_buf.end(), buf, buf + len);
         }
       }