Fix using #allTabs; it isnt a list

tabview.lua

@@ -1,4 +1,5 @@
 local parent = term.current()
+local tabCount = 0
 local allTabs = {}
 local tabOrder = {}
 local currentTab = nil
@@ -26,6 +27,7 @@ local function addTab(tab, order_idx)
     end
     allTabs[tab.name] = tab
     tabOrder[order_idx] = tab.name
+    tabCount = tabCount + 1
     return tab
 end
 
@@ -43,14 +45,14 @@ local function showTab(name)
 end
 
 local function switchTab()
-    assert(#allTabs > 0, "tabs need to be registered in order to switch tabs")
+    assert(tabCount > 0, "tabs need to be registered in order to switch tabs")
     local idx = 0
     if currentTab ~= nil then
         currentTab.window.setVisible(false)
         idx = tabOrder[currentTab.name]
     end
     idx = idx + 1
-    if idx > #allTabs then
+    if idx > tabCount then
         idx = 1
     end
     currentTab = allTabs[tabOrder[idx]]