Ensure that Annotation appearance-entries are actually Streams

Note how all over the `src/core/annotation.js`-code we're assuming that if an `appearance`-entry exists it's also a Stream. However, we're not actually checking that thoroughly enough which causes issues in some badly generated PDF documents.

src/core/annotation.js

@@ -866,7 +866,10 @@ class Annotation {
     if (!(as instanceof Name) || !normalAppearanceState.has(as.name)) {
       return;
     }
-    this.appearance = normalAppearanceState.get(as.name);
+    const appearance = normalAppearanceState.get(as.name);
+    if (appearance instanceof BaseStream) {
+      this.appearance = appearance;
+    }
   }
 
   setOptionalContent(dict) {
@@ -3013,9 +3016,12 @@ class ButtonWidgetAnnotation extends WidgetAnnotation {
 
     this.data.exportValue = exportValues[1];
 
+    const checkedAppearance = normalAppearance.get(this.data.exportValue);
     this.checkedAppearance =
-      normalAppearance.get(this.data.exportValue) || null;
-    this.uncheckedAppearance = normalAppearance.get("Off") || null;
+      checkedAppearance instanceof BaseStream ? checkedAppearance : null;
+    const uncheckedAppearance = normalAppearance.get("Off");
+    this.uncheckedAppearance =
+      uncheckedAppearance instanceof BaseStream ? uncheckedAppearance : null;
 
     if (this.checkedAppearance) {
       this._streams.push(this.checkedAppearance);
@@ -3058,9 +3064,12 @@ class ButtonWidgetAnnotation extends WidgetAnnotation {
       }
     }
 
+    const checkedAppearance = normalAppearance.get(this.data.buttonValue);
     this.checkedAppearance =
-      normalAppearance.get(this.data.buttonValue) || null;
-    this.uncheckedAppearance = normalAppearance.get("Off") || null;
+      checkedAppearance instanceof BaseStream ? checkedAppearance : null;
+    const uncheckedAppearance = normalAppearance.get("Off");
+    this.uncheckedAppearance =
+      uncheckedAppearance instanceof BaseStream ? uncheckedAppearance : null;
 
     if (this.checkedAppearance) {
       this._streams.push(this.checkedAppearance);

test/pdfs/.gitignore

@@ -21,6 +21,7 @@
 !issue14881.pdf
 !issue3214.pdf
 !issue4665.pdf
+!checkbox-bad-appearance.pdf
 !issue4684.pdf
 !issue8092.pdf
 !issue5256.pdf

test/test_manifest.json

@@ -785,6 +785,13 @@
        "rounds": 1,
        "type": "eq"
     },
+    {  "id": "checkbox-bad-appearance",
+       "file": "pdfs/checkbox-bad-appearance.pdf",
+       "md5": "acdac655911cb3d33c3fb1462cf2ad56",
+       "rounds": 1,
+       "type": "eq",
+       "forms": true
+    },
     {  "id": "artofwar",
        "file": "pdfs/artofwar.pdf",
        "md5": "7bdd51c327b74f1f7abdd90eedb2f912",