Fix empty list guard

Author: nullskill

lib/src/easy/14.longest_common_prefix/main.dart

@@ -8,7 +8,7 @@
 
 class Solution {
   String longestCommonPrefix(List<String> strs) {
-    if (strs.isEmpty) return '';
+    if (strs.join('').isEmpty) return '';
     String prefix = strs[0];
     for (int i = 1; i < strs.length; i++) {
       while (strs[i].indexOf(prefix) != 0) {