Clean up pin_tab

Also add a test case for :pin-tab with an invalid count

qutebrowser/browser/commands.py

@@ -277,16 +277,9 @@ class CommandDispatcher:
         """
         tab = self._cntwidget(count)
         if tab is None:
-            return
+            raise cmdexc.CommandError("Tab {} does not exist!".format(count))
 
         to_pin = not tab.data.pinned
-        tab_index = self._current_index() if count is None else count - 1
-        cmdutils.check_overflow(tab_index + 1, 'int')
-        tab = self._cntwidget(count)
-
-        if tab is None:
-            raise cmdexc.CommandError("Unable to find tab '{}'.".format(count))
-
         self._tabbed_browser.set_tab_pinned(tab, to_pin)
 
     @cmdutils.register(instance='command-dispatcher', name='open',

tests/end2end/features/tabs.feature

@@ -1073,6 +1073,17 @@ Feature: Tab management
             - data/numbers/2.txt (pinned)
             - data/numbers/3.txt (active)
 
+    Scenario: :tab-pin with an invalid count
+        When I open data/numbers/1.txt
+        And I open data/numbers/2.txt in a new tab
+        And I open data/numbers/3.txt in a new tab
+        And I run :tab-pin with count 23
+        Then the error "Tab 23 does not exist!" should be shown
+        And the following tabs should be open:
+            - data/numbers/1.txt
+            - data/numbers/2.txt
+            - data/numbers/3.txt (active)
+
     Scenario: Pinned :tab-close prompt yes
         When I open data/numbers/1.txt
         And I run :tab-pin