[java] BlockJoinLinesHandler: avoid removing block when there's only comment inside (IDEA-264288)

GitOrigin-RevId: dad4d5ffb573d186463589162adbd2fcd610157d

java/java-tests/testData/codeInsight/joinLines/IfBlockWithComment.java

@@ -0,0 +1,9 @@
+class C {
+  private static void fn(boolean cond) {
+    <caret>if (cond) {
+      // comment
+    } else {
+      
+    }
+  }
+}