try fix non-existent crash

Author: brachy84

src/main/java/com/cleanroommc/modularui/screen/SecondaryPanel.java

@@ -5,7 +5,6 @@
 import com.cleanroommc.modularui.widget.WidgetTree;
 
 import net.minecraft.entity.player.EntityPlayer;
-
 import net.minecraftforge.fml.relauncher.Side;
 import net.minecraftforge.fml.relauncher.SideOnly;
 
@@ -72,15 +71,14 @@ public boolean isPanelOpen() {
         return this.open;
     }
 
-    @SideOnly(Side.CLIENT)
     @Override
     public void openPanel() {
         if (this.open) return;
         if (this.screen != this.parent.getScreen()) {
             this.screen = this.parent.getScreen();
         }
         if (this.panel == null) {
-            this.panel = Objects.requireNonNull(this.provider.build(this.screen.getMainPanel(), MCHelper.getPlayer()));
+            this.panel = buildPanel();
             if (this.panel == this.screen.getMainPanel()) {
                 throw new IllegalArgumentException("Must not return main panel!");
             }
@@ -93,6 +91,11 @@ public void openPanel() {
         this.open = true;
     }
 
+    @SideOnly(Side.CLIENT)
+    private ModularPanel buildPanel() {
+        return Objects.requireNonNull(this.provider.build(this.screen.getMainPanel(), MCHelper.getPlayer()));
+    }
+
     public interface IPanelBuilder {
 
         ModularPanel build(ModularPanel parentPanel, EntityPlayer player);