Improve /Page validation for linearized documents (issue 18138)

The referenced PDF document contains corrupt linearization-data, that doesn't point to the *first* page as intended.

src/core/document.js

@@ -1576,7 +1576,10 @@ class PDFDocument {
         if (type instanceof Ref) {
           type = await xref.fetchAsync(type);
         }
-        if (isName(type, "Page") || (!obj.has("Type") && !obj.has("Kids"))) {
+        if (
+          isName(type, "Page") ||
+          (!obj.has("Type") && !obj.has("Kids") && obj.has("Contents"))
+        ) {
           if (!catalog.pageKidsCountCache.has(ref)) {
             catalog.pageKidsCountCache.put(ref, 1); // Cache the Page reference.
           }

test/pdfs/issue18138.pdf.link

@@ -0,0 +1 @@
+https://github.com/mozilla/pdf.js/files/15398373/2.pdf

test/test_manifest.json

@@ -5438,6 +5438,15 @@
     "lastPage": 1,
     "type": "eq"
   },
+  {
+    "id": "issue18138",
+    "file": "pdfs/issue18138.pdf",
+    "md5": "06136495b2dee5faed2e87c4e49d17fd",
+    "rounds": 1,
+    "link": true,
+    "lastPage": 1,
+    "type": "eq"
+  },
   {
     "id": "issue4890",
     "file": "pdfs/issue4890.pdf",