fix streams (getodk#1256)

lib/data/submission.js

@@ -43,6 +43,12 @@ const submissionXmlToFieldStream = (fields, xml, includeStructuralAttrs = false,
   const stack = new SchemaStack(fields, true);
   let textBuffer = ''; // agglomerates text nodes that come as multiple events.
   const parser = new hparser.Parser({
+    onend: () => {
+      if (!stack.hasExited()) throw new Error('Stack has not exited yet');
+
+      parser.reset();
+      outStream.push(null);
+    },
     onopentag: (name, attrs) => {
       const field = stack.push(name);
       if (field != null) {
@@ -58,18 +64,15 @@ const submissionXmlToFieldStream = (fields, xml, includeStructuralAttrs = false,
       textBuffer += text;
     },
     onclosetag: () => {
+      if (stack.hasExited()) throw new Error('Stack has already exited');
+
       const field = stack.pop();
 
       if (textBuffer !== '' || includeEmptyNodes) {
         if ((field != null) && !field.isStructural()) // don't output useless whitespace
           outStream.push({ field, text: textBuffer });
         textBuffer = '';
       }
-
-      if (stack.hasExited()) {
-        parser.reset();
-        outStream.push(null);
-      }
     }
   }, { xmlMode: true, decodeEntities: true });