Clear the input box after cancelling add reviewer action

Change-Id: I7db478f6a88de1cd8581437399b31e8f4fcd21db
diff --git a/gerrit-gwtui/src/main/java/com/google/gerrit/client/change/Reviewers.java b/gerrit-gwtui/src/main/java/com/google/gerrit/client/change/Reviewers.java
index 18e5e87..f69f406 100644
--- a/gerrit-gwtui/src/main/java/com/google/gerrit/client/change/Reviewers.java
+++ b/gerrit-gwtui/src/main/java/com/google/gerrit/client/change/Reviewers.java
@@ -134,6 +134,7 @@
     openForm.setVisible(true);
     UIObject.setVisible(form, false);
     suggestBox.setFocus(false);
+    suggestBox.setText("");
   }
 
   private void addReviewer(final String reviewer, boolean confirmed) {