修复单元格渲染报错

src/global/draw.js

@@ -794,6 +794,7 @@ function luckysheetDrawMain(scrollWidth, scrollHeight, drawWidth, drawHeight, of
 
         r = margeMaindata.r;
         c = margeMaindata.c;
+        if(r === undefined || c == undefined) break;
 
         let mainCell = Store.flowdata[r][c];