bank: Fix NPE in PostScriptFired subscriber (#12342)

The bank widget can become null before the bank build script finishes by
holding the bank close key as the bank is opened. This commit adds a
null check to avoid this possible NPE.

runelite-client/src/main/java/net/runelite/client/plugins/bank/BankPlugin.java

@@ -232,6 +232,8 @@ public class BankPlugin extends Plugin
 			final Widget[] children = bankItemContainer.getChildren();
 			long geTotal = 0, haTotal = 0;
 
+			if (children != null)
+			{
 				log.debug("Computing bank price of {} items", bankContainer.size());
 
 				// The first components are the bank items, followed by tabs etc. There are always 816 components regardless
@@ -250,6 +252,7 @@ public class BankPlugin extends Plugin
 				Widget bankTitle = client.getWidget(WidgetInfo.BANK_TITLE_BAR);
 				bankTitle.setText(bankTitle.getText() + createValueText(geTotal, haTotal));
 			}
+		}
 		else if (event.getScriptId() == ScriptID.BANKMAIN_SEARCH_REFRESH)
 		{
 			// vanilla only lays out the bank every 40 client ticks, so if the search input has changed,