fix: Font resolution logic (#437)

Closes #421.

src/font.ts

@@ -262,16 +262,23 @@ export default class FontLoader {
 
     const cachedFontResolver = new Map<number, opentype.Font | undefined>()
     const resolveFont = (word: string, fallback = true) => {
-      const code = word.charCodeAt(0)
-      if (cachedFontResolver.has(code)) return cachedFontResolver.get(code)
-
       const _fonts = [
         ...fonts,
         ...additionalFonts,
         ...specifiedLangFonts,
         ...(fallback ? nonSpecifiedLangFonts : []),
       ]
 
+      if (typeof word === 'undefined') {
+        if (fallback) {
+          return _fonts[_fonts.length - 1]
+        }
+        return undefined
+      }
+
+      const code = word.charCodeAt(0)
+      if (cachedFontResolver.has(code)) return cachedFontResolver.get(code)
+
       const font = _fonts.find((_font, index) => {
         return (
           !!_font.charToGlyphIndex(word) ||

test/language.test.tsx

@@ -1,7 +1,13 @@
 import { it, describe, expect } from 'vitest'
 
+import { initFonts, toImage } from './utils.js'
+import satori from '../src/index.js'
+
 import { detectLanguageCode } from '../src/language.js'
 
+let fonts
+initFonts((f) => (fonts = f))
+
 describe('detectLanguageCode', () => {
   it('should detect emoji', async () => {
     expect(detectLanguageCode('🔺')).toBe('emoji')
@@ -91,4 +97,20 @@ describe('detectLanguageCode', () => {
   it('should detect symbol', async () => {
     expect(detectLanguageCode('☻')).toBe('symbol')
   })
+
+  it('should not crash when rendering Arabic letters', async () => {
+    const svg = await satori(
+      <div
+        style={{
+          width: '100%',
+          height: '100%',
+          background: 'white',
+        }}
+      >
+        سلام
+      </div>,
+      { width: 100, height: 100, fonts }
+    )
+    expect(toImage(svg, 100)).toMatchImageSnapshot()
+  })
 })