[mutter] output/kms: Don't attemp to add common modes on connectors without modes

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

commit 2c8adb19660cb2cd53381372833e088962437d3b
Author: Jonas Ådahl <jadahl gmail com>
Date:   Thu Sep 29 14:23:55 2022 +0200

    output/kms: Don't attemp to add common modes on connectors without modes
    
    We have no way to sanely add safe modes if there are no modes we can
    compare with, thus don't try.
    
    Fixes the following crash:
    
     #0 are_all_modes_equally_sized at ../src/backends/native/meta-output-kms.c:284
     #1 maybe_add_fallback_modes at ../src/backends/native/meta-output-kms.c:310
     #2 init_output_modes at ../src/backends/native/meta-output-kms.c:347
     #3 meta_output_kms_new at ../src/backends/native/meta-output-kms.c:414
     #4 init_outputs at ../src/backends/native/meta-gpu-kms.c:332
     #5 meta_gpu_kms_read_current at ../src/backends/native/meta-gpu-kms.c:368
     #6 meta_gpu_kms_new at ../src/backends/native/meta-gpu-kms.c:403
     #7 create_gpu_from_udev_device at ../src/backends/native/meta-backend-native.c:461
     #8 init_gpus at ../src/backends/native/meta-backend-native.c:551
     #9 meta_backend_native_initable_init at ../src/backends/native/meta-backend-native.c:632
    
    Fixes: 877cc3eb7d44e2886395151f763ec09bea350444
    Related: https://bugzilla.redhat.com/show_bug.cgi?id=2127801
    Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/2646>

 src/backends/native/meta-output-kms.c | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/src/backends/native/meta-output-kms.c b/src/backends/native/meta-output-kms.c
index d002f1098a..0393a62178 100644
--- a/src/backends/native/meta-output-kms.c
+++ b/src/backends/native/meta-output-kms.c
@@ -342,6 +342,9 @@ maybe_add_fallback_modes (const MetaKmsConnectorState *connector_state,
                           MetaGpuKms                  *gpu_kms,
                           MetaKmsConnector            *kms_connector)
 {
+  if (!connector_state->modes)
+    return;
+
   if (!connector_state->has_scaling)
     return;