Use proper access methods in Dict.merge, rather than modifying the _map field manually

Author: Snuffleupagus

src/core/primitives.js

@@ -236,7 +236,7 @@ class Dict {
       if (!(dict instanceof Dict)) {
         continue;
       }
-      for (const [key, value] of dict._map) {
+      for (const [key, value] of dict.getRawEntries()) {
         let property = properties.get(key);
         if (property === undefined) {
           property = [];
@@ -252,20 +252,18 @@ class Dict {
     }
     for (const [name, values] of properties) {
       if (values.length === 1 || !(values[0] instanceof Dict)) {
-        mergedDict._map.set(name, values[0]);
+        mergedDict.set(name, values[0]);
         continue;
       }
       const subDict = new Dict(xref);
 
       for (const dict of values) {
-        for (const [key, value] of dict._map) {
-          if (!subDict._map.has(key)) {
-            subDict._map.set(key, value);
-          }
+        for (const [key, value] of dict.getRawEntries()) {
+          subDict.setIfNotExists(key, value);
         }
       }
       if (subDict.size > 0) {
-        mergedDict._map.set(name, subDict);
+        mergedDict.set(name, subDict);
       }
     }
     properties.clear();