gpm-kbd-backlight: Rationalize handling of battery-reduce setting

Handling of a disabled battery-reduce setting was too aggressive, which
could reduce in not setting backlight value in unrelated cases,
including initial startup and resume, as well as some cases of IDLE
handling.

Now the user choices are better followed, the whole special-casing
could probably be removed as the internal state should always reflect
the reality, but keep the specific check not to do anything on AC
plug/unplug when this is disabled just in case, although the historical
reasons why it was actually problematic should be gone now.

src/gpm-kbd-backlight.c

@@ -383,13 +383,9 @@ gpm_kbd_backlight_evaluate_power_source_and_set (GpmKbdBacklight *backlight)
    guint value;
    guint dim_by = 0;
 
-   if (up_client_get_on_battery (backlight->priv->client)) {
-      if (g_settings_get_boolean (backlight->priv->settings, GPM_SETTINGS_KBD_BACKLIGHT_BATT_REDUCE)) {
-         dim_by = g_settings_get_int (backlight->priv->settings, GPM_SETTINGS_KBD_BRIGHTNESS_DIM_BY_ON_BATT);
-      } else {
-         // do not change keyboard backlight
-         return TRUE;
-      }
+   if (up_client_get_on_battery (backlight->priv->client) &&
+       g_settings_get_boolean (backlight->priv->settings, GPM_SETTINGS_KBD_BACKLIGHT_BATT_REDUCE)) {
+      dim_by = g_settings_get_int (backlight->priv->settings, GPM_SETTINGS_KBD_BRIGHTNESS_DIM_BY_ON_BATT);
    }
 
    value = gpm_kbd_backlight_get_ac_percentage_dimmed (backlight, dim_by);
@@ -428,7 +424,9 @@ gpm_kbd_backlight_client_changed_cb (UpClient *client,
                                      GParamSpec *pspec,
                                      GpmKbdBacklight *backlight)
 {
-   gpm_kbd_backlight_evaluate_power_source_and_set (backlight);
+   if (g_settings_get_boolean (backlight->priv->settings, GPM_SETTINGS_KBD_BACKLIGHT_BATT_REDUCE)) {
+      gpm_kbd_backlight_evaluate_power_source_and_set (backlight);
+   }
 }
 
 /**
@@ -513,7 +511,6 @@ gpm_kbd_backlight_idle_changed_cb (GpmIdle *idle,
 
    enable_action = up_client_get_on_battery (backlight->priv->client)
        ? g_settings_get_boolean (backlight->priv->settings, GPM_SETTINGS_IDLE_DIM_BATT)
-         && g_settings_get_boolean (backlight->priv->settings, GPM_SETTINGS_KBD_BACKLIGHT_BATT_REDUCE)
        : g_settings_get_boolean (backlight->priv->settings, GPM_SETTINGS_IDLE_DIM_AC);
 
    if (!enable_action)