Only use base encoding if it's populated. (bug 1727053)

The font dict in this file has an encoding entry, but only specifies a
differences map. The base encoding is empty in this case and shouldn't
be used.

src/core/fonts.js

@@ -2629,7 +2629,7 @@ class Font {
           let glyphName;
           if (this.differences[charCode] !== undefined) {
             glyphName = this.differences[charCode];
-          } else if (baseEncoding[charCode] !== "") {
+          } else if (baseEncoding.length && baseEncoding[charCode] !== "") {
             glyphName = baseEncoding[charCode];
           } else {
             glyphName = StandardEncoding[charCode];

test/pdfs/.gitignore

@@ -12,6 +12,7 @@
 !xref_command_missing.pdf
 !issue1155r.pdf
 !issue2017r.pdf
+!bug1727053.pdf
 !issue2391-1.pdf
 !issue2391-2.pdf
 !issue3214.pdf

test/test_manifest.json

@@ -242,6 +242,12 @@
       "lastPage": 4,
       "type": "eq"
     },
+    {  "id": "bug1727053",
+       "file": "pdfs/bug1727053.pdf",
+       "md5": "8ed1e52da64000f9fdcb8b732f5a58f8",
+       "rounds": 1,
+       "type": "eq"
+    },
     {  "id": "issue3999",
        "file": "pdfs/issue3999.pdf",
        "md5": "0a59cd612e93758aa9f104470f45574b",