Handle empty string messages in Dart_PostCObject

runtime/vm/dart_api_message.cc

Index: runtime/vm/dart_api_message.cc
diff --git a/runtime/vm/dart_api_message.cc b/runtime/vm/dart_api_message.cc
index ed04af0f563a13f959885ccf76090623f3aaebda..18fee765b0897a63d49bb6fa1fe5c37e315c6a3c 100644
--- a/runtime/vm/dart_api_message.cc
+++ b/runtime/vm/dart_api_message.cc
@@ -1186,9 +1186,8 @@ bool ApiMessageWriter::WriteCObjectInlined(Dart_CObject* object,
         return false;
       }
 
-      Utf8::Type type;
+      Utf8::Type type = Utf8::kLatin1;
       intptr_t len = Utf8::CodeUnitCount(utf8_str, utf8_len, &type);
-      ASSERT(len > 0);
       if (len > String::kMaxElements) {
         return false;
       }