Improve output if :messages is used without errors

qutebrowser/html/log.html

@@ -37,6 +37,8 @@ th, td {
 <table>
 {{ content | safe() }}
 </table>
+{% elif content is not none %}
+<p>No messages to show.</p>
 {% else %}
 <p>Log output was disabled.</p>
 {% endif %}

tests/integration/features/misc.feature

@@ -426,3 +426,8 @@ Feature: Various utility commands.
     Scenario: Using qute:plainlog directly
         When I open qute:plainlog
         Then no crash should happen
+
+    Scenario: Using :messages without messages
+        Given I have a fresh instance
+        When I run :messages
+        Then the page should contain the plaintext "No messages to show."

tests/integration/test_invocations.py

@@ -85,3 +85,12 @@ def test_ascii_locale(httpbin, tmpdir, quteproc_new):
 
     assert len(tmpdir.listdir()) == 1
     assert (tmpdir / '?-issue908.bin').exists()
+
+
+def test_no_loglines(quteproc_new):
+    """Test qute:log with --loglines=0."""
+    quteproc_new.start(args=['--debug', '--no-err-windows', '--temp-basedir',
+                             '--loglines=0', 'about:blank'])
+    quteproc_new.open_path('qute:log')
+    quteproc_new.wait_for_load_finished('qute:log')
+    assert quteproc_new.get_content() == 'Log output was disabled.'