Handle profile.settings() return type being optional

With PyQt6-WebEngine 6.6.0 some pointer return types are now wrapped in
Optionals[]. In practice they should never be none though so I'm adding
some low effort null checking in here.

For the changes in `_SettingsWrapper` I'm not actually sure this is the
best way to be resolving this. mypy was complaining that `settings()` might be
None. How does asserting on the profile help? idk but that seems to make it
happy. Even more weirdly, none of these getters I changed seemed to be used
anywhere apart from tests. Except for getAttribute, that's used in webkit code.
Also the whole thing is checking the global default profile, generally
settings should be checked on the profile on the tab. So I think this might
just be some old code? idk, I just want to make mypy happy.

For the `init_user_agent()` change that was complaining about the profile
maybe being None.

ref: qutebrowser#7990

Author: toofar

qutebrowser/browser/webengine/webenginesettings.py

@@ -50,8 +50,12 @@ class _SettingsWrapper:
     For read operations, the default profile value is always used.
     """
 
+    def default_profile(self):
+        assert default_profile is not None
+        return default_profile
+
     def _settings(self):
-        yield default_profile.settings()
+        yield self.default_profile().settings()
         if private_profile:
             yield private_profile.settings()
 
@@ -76,19 +80,19 @@ def setUnknownUrlSchemePolicy(self, policy):
             settings.setUnknownUrlSchemePolicy(policy)
 
     def testAttribute(self, attribute):
-        return default_profile.settings().testAttribute(attribute)
+        return self.default_profile().settings().testAttribute(attribute)
 
     def fontSize(self, fonttype):
-        return default_profile.settings().fontSize(fonttype)
+        return self.default_profile().settings().fontSize(fonttype)
 
     def fontFamily(self, which):
-        return default_profile.settings().fontFamily(which)
+        return self.default_profile().settings().fontFamily(which)
 
     def defaultTextEncoding(self):
-        return default_profile.settings().defaultTextEncoding()
+        return self.default_profile().settings().defaultTextEncoding()
 
     def unknownUrlSchemePolicy(self):
-        return default_profile.settings().unknownUrlSchemePolicy()
+        return self.default_profile().settings().unknownUrlSchemePolicy()
 
 
 class WebEngineSettings(websettings.AbstractSettings):
@@ -341,7 +345,10 @@ def _init_user_agent_str(ua):
 
 
 def init_user_agent():
-    _init_user_agent_str(QWebEngineProfile.defaultProfile().httpUserAgent())
+    """Make the default WebEngine user agent available via parsed_user_agent."""
+    actual_default_profile = QWebEngineProfile.defaultProfile()
+    assert actual_default_profile is not None
+    _init_user_agent_str(actual_default_profile.httpUserAgent())
 
 
 def _init_profile(profile: QWebEngineProfile) -> None: