Fix terminal visibility when first terminal is not shown

This happened because the first terminal tab got created but since the element didn't exist
yet it wasn't marked as hidden, which caused the actual active terminal to be pushed below it.

Fixes #94714

src/vs/workbench/contrib/terminal/browser/terminalTab.ts

@@ -218,6 +218,7 @@ export class TerminalTab extends Disposable implements ITerminalTab {
 	private _terminalLocation: ViewContainerLocation = ViewContainerLocation.Panel;
 
 	private _activeInstanceIndex: number;
+	private _isVisible: boolean = false;
 
 	public get terminalInstances(): ITerminalInstance[] { return this._terminalInstances; }
 
@@ -356,6 +357,8 @@ export class TerminalTab extends Disposable implements ITerminalTab {
 			this._splitPaneContainer = newLocal;
 			this.terminalInstances.forEach(instance => this._splitPaneContainer!.split(instance));
 		}
+
+		this.setVisible(this._isVisible);
 	}
 
 	public get title(): string {
@@ -369,6 +372,7 @@ export class TerminalTab extends Disposable implements ITerminalTab {
 	}
 
 	public setVisible(visible: boolean): void {
+		this._isVisible = visible;
 		if (this._tabElement) {
 			this._tabElement.style.display = visible ? '' : 'none';
 		}