Fix screens inherited from PaginatedProjectScreen

After GWT upgrade: I3f009f3ef all screens inherited from
PaginatedProjectScreen are broken because match token wasn't
initialized and caused a NPE.

Change-Id: I525b25193a870aef4f19068d3731d68035799ea3

gerrit-gwtui/src/main/java/com/google/gerrit/client/admin/PaginatedProjectScreen.java

diff --git a/gerrit-gwtui/src/main/java/com/google/gerrit/client/admin/PaginatedProjectScreen.java b/gerrit-gwtui/src/main/java/com/google/gerrit/client/admin/PaginatedProjectScreen.java
index 6349803..66738c0 100644
--- a/gerrit-gwtui/src/main/java/com/google/gerrit/client/admin/PaginatedProjectScreen.java
+++ b/gerrit-gwtui/src/main/java/com/google/gerrit/client/admin/PaginatedProjectScreen.java
@@ -21,7 +21,7 @@
 
 abstract class PaginatedProjectScreen extends ProjectScreen {
   protected int pageSize;
-  protected String match;
+  protected String match = "";
   protected int start;
 
   PaginatedProjectScreen(Project.NameKey toShow) {