Properly read isFrontText in sign edit wrappers

Fixes #656

WrapperPlayServerOpenSignEditor and WrapperPlayClientUpdateSign
break editing the back of signs by simply calling the wrapper. The
initializers for these isFrontText fields to "true" ran AFTER the
wrappers' superclass constructor, which means that the initializers
would overwrite the value set by the "read" method.

api/src/main/java/com/github/retrooper/packetevents/wrapper/play/client/WrapperPlayClientUpdateSign.java

@@ -30,7 +30,7 @@
 public class WrapperPlayClientUpdateSign extends PacketWrapper<WrapperPlayClientUpdateSign> {
     private Vector3i blockPosition;
     private String[] textLines;
-    private boolean isFrontText = true;
+    private boolean isFrontText;
 
     public WrapperPlayClientUpdateSign(PacketReceiveEvent event) {
         super(event);
@@ -55,6 +55,8 @@ public void read() {
         }
         if (serverVersion.isNewerThanOrEquals(ServerVersion.V_1_20)) {
             isFrontText = readBoolean();
+        } else {
+            isFrontText = true;
         }
         textLines = new String[4];
         for (int i = 0; i < 4; i++) {

api/src/main/java/com/github/retrooper/packetevents/wrapper/play/server/WrapperPlayServerOpenSignEditor.java

@@ -26,7 +26,7 @@
 
 public class WrapperPlayServerOpenSignEditor extends PacketWrapper<WrapperPlayServerOpenSignEditor> {
     private Vector3i position;
-    private boolean isFrontText = true;
+    private boolean isFrontText;
 
     public WrapperPlayServerOpenSignEditor(PacketSendEvent event) {
         super(event);
@@ -50,6 +50,8 @@ public void read() {
         }
         if (serverVersion.isNewerThanOrEquals(ServerVersion.V_1_20)) {
             isFrontText = readBoolean();
+        } else {
+            isFrontText = true;
         }
     }