Adjust incorrect first obj number of "free" xref entry in `XRef_readXRefTable` (issue 7229)

Fixes 7229.

src/core/obj.js

@@ -736,6 +736,12 @@ var XRef = (function XRefClosure() {
             error('Invalid entry in XRef subsection: ' + first + ', ' + count);
           }
 
+          // The first xref table entry, i.e. obj 0, should be free. Attempting
+          // to adjust an incorrect first obj # (fixes issue 3248 and 7229).
+          if (i === 0 && entry.free && first === 1) {
+            first = 0;
+          }
+
           if (!this.entries[i + first]) {
             this.entries[i + first] = entry;
           }
@@ -749,12 +755,6 @@ var XRef = (function XRefClosure() {
         delete tableState.entryCount;
       }
 
-      // Per issue 3248: hp scanners generate bad XRef
-      if (first === 1 && this.entries[1] && this.entries[1].free) {
-        // shifting the entries
-        this.entries.shift();
-      }
-
       // Sanity check: as per spec, first object must be free
       if (this.entries[0] && !this.entries[0].free) {
         error('Invalid XRef table: unexpected first object');

test/pdfs/.gitignore

@@ -24,6 +24,7 @@
 !issue7101.pdf
 !issue7115.pdf
 !issue7200.pdf
+!issue7229.pdf
 !filled-background.pdf
 !ArabicCIDTrueType.pdf
 !ThuluthFeatures.pdf

test/test_manifest.json

@@ -1248,6 +1248,14 @@
        "lastPage": 1,
        "type": "eq"
     },
+    {  "id": "issue7229",
+       "file": "pdfs/issue7229.pdf",
+       "md5": "480e51aae0ac271780e4603d1561d15e",
+       "rounds": 1,
+       "link": false,
+       "lastPage": 1,
+       "type": "load"
+    },
     {  "id": "issue1940",
        "file": "pdfs/issue1940.pdf",
        "md5": "4f0a0b92c1b5e6e86e1a82490087e6e5",