composer: Fix corruption issue due to wrong index

Fix vector corruption issue due to wrong index

Change-Id: Ia9a4d2b5227e1732421e5adf33a9d32b345c8c67
diff --git a/composer/QtiComposerClient.cpp b/composer/QtiComposerClient.cpp
index 2d37d74..b772193 100644
--- a/composer/QtiComposerClient.cpp
+++ b/composer/QtiComposerClient.cpp
@@ -1996,7 +1996,7 @@
   for (const auto& m : metadata) {
     keys.push_back(static_cast<int32_t>(m.key));
     sizes_of_metablob_.push_back(m.blob.size());
-    for (uint8_t i = 0; i < m.blob.size(); i++) {
+    for (size_t i = 0; i < m.blob.size(); i++) {
       blob_of_data_.push_back(m.blob[i]);
     }
   }