Fix crash with :tab-{prev,next,focus} with 0 tabs

When using :tab-prev/:tab-next (or :tab-focus which uses :tab-next
internally) immediately after the last tab, those functions could be
called with 0 tabs open, which caused a ZeroDivisionError when trying to
do % 0.

Fixes #1448.

CHANGELOG.asciidoc

@@ -36,6 +36,13 @@ Changed
   the right.
 - `:yank` can now yank the pretty/decoded URL by adding `--pretty`
 
+Fixed
+~~~~~
+
+- Fixed crash when using `:tab-{prev,next,focus}` right after closing the last
+  tab with `last-close` set to `close`.
+
+
 v0.6.1
 -----
 

qutebrowser/browser/commands.py

@@ -785,6 +785,10 @@ class CommandDispatcher:
         Args:
             count: How many tabs to switch back.
         """
+        if self._count() == 0:
+            # Running :tab-prev after last tab was closed
+            # See https://github.com/The-Compiler/qutebrowser/issues/1448
+            return
         newidx = self._current_index() - count
         if newidx >= 0:
             self._set_current_index(newidx)
@@ -801,6 +805,10 @@ class CommandDispatcher:
         Args:
             count: How many tabs to switch forward.
         """
+        if self._count() == 0:
+            # Running :tab-next after last tab was closed
+            # See https://github.com/The-Compiler/qutebrowser/issues/1448
+            return
         newidx = self._current_index() + count
         if newidx < self._count():
             self._set_current_index(newidx)

tests/integration/features/tabs.feature

@@ -851,3 +851,17 @@ Feature: Tab management
         When I open data/title.html
         And I run :buffer "1/2/3"
         Then the error "No matching tab for: 1/2/3" should be shown
+        
+    Scenario: Using :tab-next after closing last tab (#1448)
+        When I set tabs -> last-close to close
+        And I run :tab-only
+        And I run :tab-close ;; :tab-next
+        Then qutebrowser should quit
+        And no crash should happen
+
+    Scenario: Using :tab-prev after closing last tab (#1448)
+        When I set tabs -> last-close to close
+        And I run :tab-only
+        And I run :tab-close ;; :tab-prev
+        Then qutebrowser should quit
+        And no crash should happen