Merge pull request #6848 from Snuffleupagus/recover-missing-glyf-table

[TrueType] Recover from a missing "glyf" table by replacing it with dummy data, utilizing the existing code in `sanitizeGlyphLocations`

src/core/fonts.js

@@ -4154,8 +4154,16 @@ var Font = (function FontClosure() {
         delete tables['cvt '];
         this.isOpenType = true;
       } else {
-        if (!tables.glyf || !tables.loca) {
+        if (!tables.loca) {
-          error('Required "glyf" or "loca" tables are not found');
+          error('Required "loca" table is not found');
+        }
+        if (!tables.glyf) {
+          warn('Required "glyf" table is not found -- trying to recover.');
+          // Note: We use `sanitizeGlyphLocations` to add dummy glyf data below.
+          tables.glyf = {
+            tag: 'glyf',
+            data: new Uint8Array(0),
+          };
         }
         this.isOpenType = false;
       }

test/pdfs/.gitignore

@@ -11,6 +11,7 @@
 !issue2391-1.pdf
 !issue2391-2.pdf
 !issue4665.pdf
+!issue4684.pdf
 !issue5801.pdf
 !issue5946.pdf
 !issue5972.pdf

test/test_manifest.json

@@ -1789,6 +1789,14 @@
       "type": "eq",
       "about": "Has a multi-byte char codes."
     },
+    {  "id": "issue4684-text",
+       "file": "pdfs/issue4684.pdf",
+       "md5": "af5056fcdfb08bd7adc1710d36e4b5b5",
+       "link": false,
+       "rounds": 1,
+       "type": "text",
+       "about": "Invisible (and broken) TrueType font used for text-selection."
+    },
     {  "id": "issue1912",
       "file": "pdfs/issue1912.pdf",
       "md5": "15305b7c2cba971e7423de3f6ad38fef",