Index: ps/trunk/binaries/data/mods/public/gui/common/tab_buttons.js
===================================================================
--- ps/trunk/binaries/data/mods/public/gui/common/tab_buttons.js	(revision 20967)
+++ ps/trunk/binaries/data/mods/public/gui/common/tab_buttons.js	(revision 20968)
@@ -1,75 +1,76 @@
 /**
  * Number of categories.
  */
 var g_TabCategoryCount;
 
 /**
  * Index of the currently visible tab, set first tab as default.
  */
 var g_TabCategorySelected = 0;
 
 /**
  * Function to be executed when selecting a tab. The new category index is passed.
  */
 var g_OnSelectTab;
 
 /**
  * Create tab buttons.
  *
  * @param {Array} categoriesData - Arrays of objects containing for every tab a (translated) label and tooltip.
  * @param {number} buttonHeight - Vertical distance between the top and bottom of a button.
  * @param {number} spacing - Vertical distance between two buttons.
  * @param {function} onPress - Function to be executed when a button is pressed, it gets the new category index passed.
  * @param {function} onSelect - Function to be executed whenever the selection changes (so also for scrolling), it gets the new category index passed.
  */
 function placeTabButtons(categoriesData, buttonHeight, spacing, onPress, onSelect)
 {
 	g_OnSelectTab = onSelect;
 	g_TabCategoryCount = categoriesData.length;
 
 	for (let category in categoriesData)
 	{
 		let button = Engine.GetGUIObjectByName("tabButton[" + category + "]");
 		if (!button)
 		{
 			warn("Too few tab-buttons!");
 			break;
 		}
 
 		button.hidden = false;
 
 		let size = button.size;
 		size.top = category * (buttonHeight + spacing) + spacing / 2;
 		size.bottom = size.top + buttonHeight;
 		button.size = size;
 		button.tooltip = categoriesData[category].tooltip || "";
 		button.onPress = (category => function() { onPress(category); })(+category);
 
 		Engine.GetGUIObjectByName("tabButtonText[" + category + "]").caption = categoriesData[category].label;
 	}
 
 	selectPanel(g_TabCategorySelected);
 }
 
 /**
  * Show next/previous panel.
  * @param direction - +1/-1 for forward/backward.
  */
 function selectNextTab(direction)
 {
-	selectPanel(g_TabCategorySelected === undefined ?
-		direction > 0 ?
-			0 :
-			g_TabCategoryCount - 1 :
-		(g_TabCategorySelected + direction + g_TabCategoryCount) % g_TabCategoryCount);
+	if (g_TabCategoryCount)
+		selectPanel(g_TabCategorySelected === undefined ?
+			direction > 0 ?
+				0 :
+				g_TabCategoryCount - 1 :
+			(g_TabCategorySelected + direction + g_TabCategoryCount) % g_TabCategoryCount);
 }
 
 function selectPanel(category)
 {
 	g_TabCategorySelected = category;
 	Engine.GetGUIObjectByName("tabButtons").children.forEach((button, j) => {
 		button.sprite = category == j ? "ModernTabVerticalForeground" : "ModernTabVerticalBackground";
 	});
 
 	g_OnSelectTab(category);
 }