[mutter] color-device: Don't attempt to set GAMMA_LUT if LUT size is zero

[Marge Bot <marge-bot src gnome org>]

commit 255cd9a9fff5d928eb63eb3464b5d4c27a2a74e4
Author: Jonas Ådahl <jadahl gmail com>
Date:   Sat Sep 3 15:01:40 2022 +0200

    color-device: Don't attempt to set GAMMA_LUT if LUT size is zero
    
    This might happen on e.g. virtual machines. If we don't skip trying,
    we'll end up crashing because we'll fail to create a look up table since
    the size must be greater than zero to make any sense.
    
    Fixes: baef39e603f232f5ce3c2ce79c443383cd6a1f67
    Closes: https://gitlab.gnome.org/GNOME/mutter/-/issues/2415
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2611>

 src/backends/meta-color-device.c  | 14 +++++++++-----
 src/backends/meta-color-profile.c |  2 +-
 2 files changed, 10 insertions(+), 6 deletions(-)
---
diff --git a/src/backends/meta-color-device.c b/src/backends/meta-color-device.c
index 272fade579..e6854fc3a6 100644
--- a/src/backends/meta-color-device.c
+++ b/src/backends/meta-color-device.c
@@ -1171,7 +1171,6 @@ meta_color_device_update (MetaColorDevice *color_device,
   MetaColorProfile *color_profile;
   MetaMonitor *monitor;
   size_t lut_size;
-  g_autoptr (MetaGammaLut) lut = NULL;
 
   color_profile = meta_color_device_get_assigned_profile (color_device);
   if (!color_profile)
@@ -1206,11 +1205,16 @@ meta_color_device_update (MetaColorDevice *color_device,
     }
 
   lut_size = meta_monitor_get_gamma_lut_size (monitor);
-  lut = meta_color_profile_generate_gamma_lut (color_profile,
-                                               temperature,
-                                               lut_size);
+  if (lut_size > 0)
+    {
+      g_autoptr (MetaGammaLut) lut = NULL;
+
+      lut = meta_color_profile_generate_gamma_lut (color_profile,
+                                                   temperature,
+                                                   lut_size);
 
-  meta_monitor_set_gamma_lut (monitor, lut);
+      meta_monitor_set_gamma_lut (monitor, lut);
+    }
 
   g_signal_emit (color_device, signals[UPDATED], 0);
 }
diff --git a/src/backends/meta-color-profile.c b/src/backends/meta-color-profile.c
index 573acadb86..82c235b0f4 100644
--- a/src/backends/meta-color-profile.c
+++ b/src/backends/meta-color-profile.c
@@ -488,7 +488,7 @@ meta_color_profile_generate_gamma_lut (MetaColorProfile *color_profile,
                                        unsigned int      temperature,
                                        size_t            lut_size)
 {
-  g_return_val_if_fail (lut_size > 0, NULL);
+  g_assert (lut_size > 0);
 
   if (color_profile->calibration->has_vcgt)
     {