Don't double set library method override.

Change-Id: Idf37d352b1ab02d87fa2445d8b64889e4f68338f
diff --git a/src/main/java/com/android/tools/r8/shaking/Enqueuer.java b/src/main/java/com/android/tools/r8/shaking/Enqueuer.java
index 3d9c1c9..2b5cdde 100644
--- a/src/main/java/com/android/tools/r8/shaking/Enqueuer.java
+++ b/src/main/java/com/android/tools/r8/shaking/Enqueuer.java
@@ -1848,6 +1848,9 @@
   private void markOverridesAsLibraryMethodOverrides(
       DexProgramClass holder, DexEncodedMethod libraryMethodOverride) {
     assert holder.type == libraryMethodOverride.holder();
+    if (libraryMethodOverride.isLibraryMethodOverride().isTrue()) {
+      return;
+    }
     libraryMethodOverride.setLibraryMethodOverride(OptionalBool.TRUE);
     WorkList<DexType> worklist = WorkList.newIdentityWorkList();
     holder.forEachImmediateSupertype(worklist::addIfNotSeen);