Fix MSVC warnings about possible value truncation.

src/loca.cc

Index: src/loca.cc
diff --git a/src/loca.cc b/src/loca.cc
index a2947b279922992712e316d478916196e1d033a1..ad74b267354d3f6d9e41517831b5fe3a364920d5 100644
--- a/src/loca.cc
+++ b/src/loca.cc
@@ -76,7 +76,9 @@ bool ots_loca_serialise(OTSStream *out, OpenTypeFile *file) {
 
   if (head->index_to_loc_format == 0) {
     for (unsigned i = 0; i < loca->offsets.size(); ++i) {
-      if (!out->WriteU16(loca->offsets[i] >> 1)) {
+      const uint16_t offset = static_cast<uint16_t>(loca->offsets[i] >> 1);
+      if ((offset != (loca->offsets[i] >> 1)) ||
+          !out->WriteU16(offset)) {
         return OTS_FAILURE();
       }
     }