Fix loading of fonts with empty font files (bug 866395 and issue 3522)

src/core/fonts.js

@@ -2204,7 +2204,13 @@ var Font = (function FontClosure() {
       this.defaultVMetrics = properties.defaultVMetrics;
     }
 
-    if (!file) {
+    if (!file || file.isEmpty) {
+      if (file) {
+        // Some bad PDF generators will include empty font files,
+        // attempting to recover by assuming that no file exists.
+        warn('Font file is empty in "' + name + '" (' + this.loadedName + ')');
+      }
+
       this.missingFile = true;
       // The file data is not specified. Trying to fix the font name
       // to be used with the canvas.font.

test/pdfs/.gitignore

@@ -55,6 +55,7 @@
 !gradientfill.pdf
 !bug903856.pdf
 !bug850854.pdf
+!bug866395.pdf
 !basicapi.pdf
 !mixedfonts.pdf
 !shading_extend.pdf

test/test_manifest.json

@@ -682,6 +682,14 @@
        "type": "eq",
        "about": "Seac with differences array that messes up mapping."
     },
+    {  "id": "bug866395",
+       "file": "pdfs/bug866395.pdf",
+       "md5": "f03bc77e84637241980b09a0a220f575",
+       "link": false,
+       "rounds": 1,
+       "type": "eq",
+       "about": "Font with an empty font file."
+    },
     {  "id": "ocs",
       "file": "pdfs/ocs.pdf",
       "md5": "2ade57e954ae7632749cf328daeaa7a8",