Fix generator bug when oneof is first field in a message.

Added test case for the same.

Update issue 142
Status: FixedInGit

tests/oneof/oneof.proto

@@ -5,6 +5,7 @@ message SubMessage
     repeated int32 array = 1 [(nanopb).max_count = 8];
 }
 
+/* Oneof in a message with other fields */
 message OneOfMessage
 {
     required int32 prefix = 1;
@@ -16,3 +17,14 @@ message OneOfMessage
     }
     required int32 suffix = 99;
 }
+
+/* Oneof in a message by itself */
+message PlainOneOfMessage
+{
+    oneof values
+    {
+        int32 first = 5;
+        string second = 6 [(nanopb).max_size = 8];
+        SubMessage third = 7;
+    }
+}