Issue 25219. Fix for RangeError during converting empty lines in /// comments.

pkg/analysis_server/lib/src/services/correction/assist_internal.dart

Index: pkg/analysis_server/lib/src/services/correction/assist_internal.dart
diff --git a/pkg/analysis_server/lib/src/services/correction/assist_internal.dart b/pkg/analysis_server/lib/src/services/correction/assist_internal.dart
index c6f1c020ad004e82b583dc7fb08559ea026b9f82..00c48a340a3ea823b85506805fdb56cde9114d8e 100644
--- a/pkg/analysis_server/lib/src/services/correction/assist_internal.dart
+++ b/pkg/analysis_server/lib/src/services/correction/assist_internal.dart
@@ -413,8 +413,8 @@ class AssistProcessor {
         if (token is DocumentationCommentToken &&
             token.type == TokenType.SINGLE_LINE_COMMENT) {
           sb.append(prefix);
-          sb.append(' * ');
-          sb.append(token.lexeme.substring('/// '.length));
+          sb.append(' *');
+          sb.append(token.lexeme.substring('///'.length));
           sb.append(eol);
         } else {
           return;