Don't clobber existing std handles when attaching to the parent console

Fixes #1270

app/main.cpp

@@ -559,16 +559,19 @@ int main(int argc, char *argv[])
         s_SuppressVerboseOutput = true;
 #endif
 #ifdef Q_OS_WIN32
-        // Attach to the console to be able to print output.
-        // Since we're a /SUBSYSTEM:WINDOWS app, we won't be attached by default.
+        // If we don't have stdout or stderr handles (which will normally be the case
+        // since we're a /SUBSYSTEM:WINDOWS app), attach to our parent console and use
+        // that for stdout and stderr.
+        //
+        // If we do have stdout or stderr handles, that means the user has used standard
+        // handle redirection. In that case, we don't want to override those handles.
         if (AttachConsole(ATTACH_PARENT_PROCESS)) {
-            HANDLE conOut = GetStdHandle(STD_OUTPUT_HANDLE);
-            if (conOut != INVALID_HANDLE_VALUE && conOut != NULL) {
+            // If we didn't have an old stdout/stderr handle, use the new CONOUT$ handle
+            if (IS_UNSPECIFIED_HANDLE(oldConOut)) {
                 freopen("CONOUT$", "w", stdout);
                 setvbuf(stdout, NULL, _IONBF, 0);
             }
-            HANDLE conErr = GetStdHandle(STD_ERROR_HANDLE);
-            if (conErr != INVALID_HANDLE_VALUE && conErr != NULL) {
+            if (IS_UNSPECIFIED_HANDLE(oldConErr)) {
                 freopen("CONOUT$", "w", stderr);
                 setvbuf(stderr, NULL, _IONBF, 0);
             }
@@ -762,5 +765,12 @@ int main(int argc, char *argv[])
     // sometimes freezing and blocking process exit.
     QThreadPool::globalInstance()->waitForDone(30000);
 
+#ifdef Q_OS_WIN32
+    // Without an explicit flush, console redirection for the list command
+    // doesn't work reliably (sometimes the target file contains no text).
+    fflush(stderr);
+    fflush(stdout);
+#endif
+
     return err;
 }