[mutter/cherry-pick-2c8adb19] output/kms: Don't attemp to add common modes on connectors without modes

[Jonas Ådahl <jadahl src gnome org>]

commit 6698a96b9fadcb2db1058b0afefb8ccfea377b11
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>
    
    
    (cherry picked from commit 2c8adb19660cb2cd53381372833e088962437d3b)

 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 91a4ccaed7..d9943dbf42 100644
--- a/src/backends/native/meta-output-kms.c
+++ b/src/backends/native/meta-output-kms.c
@@ -303,6 +303,9 @@ 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;