guard against empty entity lists

Unable to repro the reported issue, but this will at least protect against the exception.

Fixes: https://dart-review.googlesource.com/c/sdk/+/359280

Change-Id: I712f9b92879ca6b80b2f1004206e4f77a3178a47
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/359280
Reviewed-by: Keerti Parthasarathy <[email protected]>
Commit-Queue: Phil Quitslund <[email protected]>

Author: pq

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

@@ -34,6 +34,7 @@ class SplitMultipleDeclarations extends ResolvedCorrectionProducer {
     final hasMetadata = variableList.metadata.isNotEmpty;
 
     final parent = variableList.parent;
+    // TODO(sstasi95): consider fields
     final hasParentMetadata =
         (parent is TopLevelVariableDeclaration) && parent.metadata.isNotEmpty;
 
@@ -49,6 +50,10 @@ class SplitMultipleDeclarations extends ResolvedCorrectionProducer {
 
     final entities = variableList.childEntities
         .where((e) => e is KeywordToken || e is NamedType);
+    if (entities.isEmpty) {
+      return;
+    }
+
     final entitiesRange = range.startEnd(entities.first, entities.last);
     final keywordsAndType = utils.getRangeText(entitiesRange);