Partially reverts #2239 due to reftest fails

src/fonts.js

@@ -3557,10 +3557,6 @@ var Font = (function FontClosure() {
         this.glyphNameMap = properties.glyphNameMap;
       }
 
-      if (ids.length === 0) {
-        error('Valid glyph data is not found');
-      }
-
       // Converting glyphs and ids into font's cmap table
       cmap.data = createCMapTable(glyphs, ids);
       var unicodeIsEnabled = [];