fix svg font export bug

src/ttf/svg2ttfobject.js

@@ -41,6 +41,7 @@ define(
          */
         function getEmptyObject() {
             return {
+                'from': 'svg',
                 'OS/2': {},
                 'name': {},
                 'hhea': {},

src/ttf/table/OS2.js

@@ -228,12 +228,15 @@ define(
                     ttf['OS/2'].usLastCharIndex = usLastCharIndex;
 
                     // rewrite hhea
+                    ttf.hhea.version = ttf.hhea.version || 0x1;
                     ttf.hhea.advanceWidthMax = advanceWidthMax;
                     ttf.hhea.minLeftSideBearing = minLeftSideBearing;
                     ttf.hhea.minRightSideBearing = minRightSideBearing;
                     ttf.hhea.xMaxExtent = xMaxExtent;
 
                     // rewrite head
+                    ttf.head.version = ttf.head.version || 0x1;
+                    ttf.head.lowestRecPPEM = ttf.head.lowestRecPPEM || 0x8;
                     ttf.head.xMin = xMin;
                     ttf.head.yMin = yMin;
                     ttf.head.xMax = xMax;

src/ttf/table/post.js

@@ -135,6 +135,7 @@ define(
                     }
 
                     ttf.post = ttf.post || {};
+                    ttf.post.format = ttf.post.format || 0x2;
                     ttf.post.maxMemType1 = numberOfGlyphs;
 
                     ttf.support.post = {

src/ttf/ttfwriter.js

@@ -42,6 +42,7 @@ define(
         function resolve(ttf) {
 
             // 头部信息
+            ttf.version = ttf.version || 0x1;
             ttf.numTables = tableList.length;
             ttf.entrySelector = Math.floor(Math.log(tableList.length)/Math.LN2);
             ttf.searchRange = Math.pow(2, ttf.entrySelector) * 16;