Fix crash when doing :<space><enter>

Introduced in #1577.
Fixes #1773.

CHANGELOG.asciidoc

@@ -45,6 +45,14 @@ Changed
 - `:download-open` and `:prompt-open-download` now have an optional `cmdline`
   argument to pass a commandline to open the download with.
 
+v0.8.3 (unreleased)
+-------------------
+
+Fixed
+~~~~~
+
+- Fixed crash when doing `:<space><enter>`, another corner-case introduced in v0.8.0
+
 v0.8.2
 ------
 

qutebrowser/commands/runners.py

@@ -119,7 +119,7 @@ class CommandRunner(QObject):
         Yields:
             ParseResult tuples.
         """
-        if not text:
+        if not text.strip():
             raise cmdexc.NoSuchCommandError("No command given")
 
         if aliases:

tests/unit/commands/test_runners.py

@@ -53,14 +53,16 @@ class TestCommandRunner:
             with pytest.raises(cmdexc.NoSuchCommandError):
                 list(cr.parse_all("alias_name"))
 
-    def test_parse_empty_with_alias(self):
+    @pytest.mark.parametrize('command', ['', ' '])
+    def test_parse_empty_with_alias(self, command):
         """An empty command should not crash.
 
         See https://github.com/The-Compiler/qutebrowser/issues/1690
+        and https://github.com/The-Compiler/qutebrowser/issues/1773
         """
         cr = runners.CommandRunner(0)
         with pytest.raises(cmdexc.NoSuchCommandError):
-            list(cr.parse_all(''))
+            list(cr.parse_all(command))
 
     def test_parse_with_count(self):
         """Test parsing of commands with a count."""