--verbose & GS_DEBUG ignored when stderr is journald

As previously discussed on #2082 (comment 1679187) I would like to arrange for Software to always emit verbose output, so that I can more easily diagnose issues & write useful bug reports.

Typically gnome-software's stderr is connected to the journal. This is what I want – to be able to look back at the journal when something weird has happened.

However, when gnome-software detects that its stderr is journald, it invokes a different log writer function which forwards ERROR, CRITICAL, WARNING and INFO-grade log messages to the journal, and discards everything else. It does this regardless of whether the verbose flag has been set (whether via --verbose or via the GS_DEBUG environment variable).

Before 82d3664c, all messages at those 4 levels were always logged to the journal, regardless of whether stderr was or was not the journal. (Objectively weird behaviour.)

I think something more like this would be more appropriate:

diff --git a/lib/gs-debug.c b/lib/gs-debug.c
index 9d755967d..5828394f3 100644
--- a/lib/gs-debug.c
+++ b/lib/gs-debug.c
@@ -146,6 +146,8 @@ gs_log_writer_journald (GLogLevelFlags log_level,
                         gsize n_fields,
                         gpointer user_data)
 {
+       GsDebug *debug = GS_DEBUG (user_data);
+
        /* important enough to force to the journal */
        switch (log_level) {
        case G_LOG_LEVEL_ERROR:
@@ -154,6 +156,12 @@ gs_log_writer_journald (GLogLevelFlags log_level,
        case G_LOG_LEVEL_INFO:
                return g_log_writer_journald (log_level, fields, n_fields, user_data);
                break;
+
+       case G_LOG_LEVEL_DEBUG:
+               if (g_atomic_int_get (&debug->verbose))
+                       return g_log_writer_journald (log_level, fields, n_fields, user_data);
+               break;
+
        default:
                break;
        }

(as an aside: what about G_LOG_LEVEL_MESSAGE?)