feat: 判断xml里是否有渐变标示，增加处理逻辑

src/views/music-library/music-sheet/modal/music-operationV2.tsx

@@ -226,6 +226,8 @@ export function getGradualLengthByXml(xml: string) {
     }
 
     const isKeyWork = keys.find((k) => {
+      // 排除单个字母的情况
+      if (!textContent || textContent.length <= 1) return false
       const ks = k.split(' ')
       return textContent && ks.includes(textContent) || k === textContent
     })