Fix redundantBlock in StringBuilderOptimizer

Change-Id: I8fe0c210652425e3bf828a5130d43ac4a527a84a
diff --git a/src/main/java/com/android/tools/r8/ir/optimize/string/StringBuilderAppendOptimizer.java b/src/main/java/com/android/tools/r8/ir/optimize/string/StringBuilderAppendOptimizer.java
index 5ed16f7..2bc3346 100644
--- a/src/main/java/com/android/tools/r8/ir/optimize/string/StringBuilderAppendOptimizer.java
+++ b/src/main/java/com/android/tools/r8/ir/optimize/string/StringBuilderAppendOptimizer.java
@@ -117,6 +117,8 @@
       }
     }
     code.removeAllDeadAndTrivialPhis();
+    code.removeRedundantBlocks();
+    assert code.isConsistentSSA(appView);
     return CodeRewriterResult.HAS_CHANGED;
   }