Check if sys.stdout is not None before using it.

When using pythonw (e.g. with cx_Freeze), sys.__stdout__ and sys.stdout
will be None, so we don't need to flush it.

This also means faulthandler won't work correctly, so we don't enabled
it if we don't have an stdout.

qutebrowser/app.py

@@ -19,6 +19,8 @@
 
 ### Things we want to do before normal imports ###
 
+import sys
+
 # Print a nice traceback on segfault -- only available on Python 3.3+, but if
 # it's unavailable, it doesn't matter much.
 try:
@@ -26,7 +28,16 @@ try:
 except ImportError:
     pass
 else:
-    faulthandler.enable()
+    if sys.__stdout__ is not None:
+        # When run with pythonw.exe, sys.__stdout__ can be None:
+        # https://docs.python.org/3/library/sys.html#sys.__stdout__
+        # If we'd enable faulthandler in that case, we just get a weird
+        # exception, so we don't enable faulthandler in that case.
+        #
+        # FIXME at the point we have our config/data dirs, we probably should
+        # re-enable faulthandler to write to a file. Then we can also display
+        # crashes to the user at the next start.
+        faulthandler.enable()
 
 # See https://bugreports.qt-project.org/browse/QTBUG-36099
 # We need to do this before importing PyQt
@@ -37,8 +48,8 @@ harfbuzz.fix()
 import qutebrowser.utils.dependencies as dependencies
 dependencies.check()
 
+# Early imports done, normal imports following now.
 import os
-import sys
 import logging
 import subprocess
 import configparser

qutebrowser/utils/debug.py

@@ -56,7 +56,8 @@ def set_trace():
 
     Based on http://stackoverflow.com/a/1745965/2085149
     """
-    sys.stdout.flush()
+    if sys.stdout is not None:
+        sys.stdout.flush()
     print()
     print("When done debugging, remember to execute:")
     print("  from PyQt5 import QtCore; QtCore.pyqtRestoreInputHook()")

qutebrowser/utils/misc.py

@@ -167,7 +167,8 @@ def actute_warning():
     with open('/usr/share/X11/locale/en_US.UTF-8/Compose', 'r') as f:
         for line in f:
             if '<dead_actute>' in line:
-                sys.stdout.flush()
+                if sys.stdout is not None:
+                    sys.stdout.flush()
                 print("Note: If you got a 'dead_actute' warning above, that "
                       "is not a bug in qutebrowser! See "
                       "https://bugs.freedesktop.org/show_bug.cgi?id=69476 for "