Fix MSVC warnings about possible value truncation.

src/ltsh.cc

Index: src/ltsh.cc
diff --git a/src/ltsh.cc b/src/ltsh.cc
index 9145527dc745ed670a78053bf9f67c03f4dba950..16700daa7ab33cd2120648af5d051e48b9a223a9 100644
--- a/src/ltsh.cc
+++ b/src/ltsh.cc
@@ -61,12 +61,13 @@ bool ots_ltsh_should_serialise(OpenTypeFile *file) {
 
 bool ots_ltsh_serialise(OTSStream *out, OpenTypeFile *file) {
   const OpenTypeLTSH *ltsh = file->ltsh;
-
-  if (!out->WriteU16(ltsh->version) ||
-      !out->WriteU16(ltsh->ypels.size())) {
+  const uint16_t num_ypels = static_cast<uint16_t>(ltsh->ypels.size());
+  if (num_ypels != ltsh->ypels.size() ||
+      !out->WriteU16(ltsh->version) ||
+      !out->WriteU16(num_ypels)) {
     return OTS_FAILURE();
   }
-  for (unsigned i = 0; i < ltsh->ypels.size(); ++i) {
+  for (uint16_t i = 0; i < num_ypels; ++i) {
     if (!out->Write(&(ltsh->ypels[i]), 1)) {
       return OTS_FAILURE();
     }