Fix MSVC warnings about possible value truncation.

src/vorg.cc

Index: src/vorg.cc
diff --git a/src/vorg.cc b/src/vorg.cc
index 61658fda61232434634c7a48d37187e808004026..b218c8895e4070bc5ce21e9c24df0fc1a3513eb8 100644
--- a/src/vorg.cc
+++ b/src/vorg.cc
@@ -71,15 +71,17 @@ bool ots_vorg_should_serialise(OpenTypeFile *file) {
 
 bool ots_vorg_serialise(OTSStream *out, OpenTypeFile *file) {
   OpenTypeVORG * const vorg = file->vorg;
-
-  if (!out->WriteU16(vorg->major_version) ||
+  
+  const uint16_t num_metrics = static_cast<uint16_t>(vorg->metrics.size());
+  if (num_metrics != vorg->metrics.size() ||
+      !out->WriteU16(vorg->major_version) ||
       !out->WriteU16(vorg->minor_version) ||
       !out->WriteS16(vorg->default_vert_origin_y) ||
-      !out->WriteU16(vorg->metrics.size())) {
+      !out->WriteU16(num_metrics)) {
     return OTS_FAILURE();
   }
 
-  for (unsigned i = 0; i < vorg->metrics.size(); ++i) {
+  for (uint16_t i = 0; i < num_metrics; ++i) {
     const OpenTypeVORGMetrics& rec = vorg->metrics[i];
     if (!out->WriteU16(rec.glyph_index) ||
         !out->WriteS16(rec.vert_origin_y)) {