Improve debug logging in case of unexpected Win32 error

test_configuration_loader.deleting_parent_of_missing_file_is_not_detected_as_a_change
is a flaky test on Windows [1]. I haven't been able to reproduce the
failure on my machine. Add some logging to we can better debug the issue
if the test fails on CI again.

[1] #479

Author: strager

src/change-detecting-filesystem-win32.cpp

@@ -139,6 +139,10 @@ bool change_detecting_filesystem_win32::handle_event(
     return false;
 
   default:
+    std::fprintf(stderr,
+                 "error: change_detecting_filesystem_win32 received unexpected "
+                 "error: %u (number_of_bytes_transferred=%u)\n",
+                 error, number_of_bytes_transferred);
     QLJS_UNIMPLEMENTED();
     return true;
   }