IDEA-136783 Completion: delay showing middle-matched items until at least some (or all) start-matching ones are shown

avoid useless allocations

platform/lang-impl/src/com/intellij/codeInsight/completion/CompletionProgressIndicator.java

@@ -426,6 +426,7 @@ public class CompletionProgressIndicator extends ProgressIndicatorBase implement
   void addDelayedMiddleMatches() {
     ArrayList<CompletionResult> delayed;
     synchronized (myDelayedMiddleMatches) {
+      if (myDelayedMiddleMatches.isEmpty()) return;
       delayed = ContainerUtil.newArrayList(myDelayedMiddleMatches);
       myDelayedMiddleMatches.clear();
     }