Disable merging of 'if' statements when there are other staments in the outer one.

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 abad641b62f21daa9145920773b43b2425436f92..c6f1c020ad004e82b583dc7fb08559ea026b9f82 100644
--- a/pkg/analysis_server/lib/src/services/correction/assist_internal.dart
+++ b/pkg/analysis_server/lib/src/services/correction/assist_internal.dart
@@ -1251,6 +1251,10 @@ class AssistProcessor {
     // prepare outer "if" statement
     AstNode parent = targetIfStatement.parent;
     if (parent is Block) {
+      if ((parent as Block).statements.length != 1) {
+        _coverageMarker();
+        return;
+      }
       parent = parent.parent;
     }
     if (parent is! IfStatement) {