[mutter/wip/carlosg/maybe-uninitialized: 3/3] backends/native: Avoid -Wmaybe-uninitialized warning

[Carlos Garnacho <carlosg src gnome org>]

commit b9b98db7d1f88d7f57e73ac00d9714509e8ff555
Author: Carlos Garnacho <carlosg gnome org>
Date:   Fri Dec 4 16:17:16 2020 +0100

    backends/native: Avoid -Wmaybe-uninitialized warning
    
    Ensure that color_ptr gets set, and avoid color_char usage too in
    that case. Fixes:
    
      ../../../../Source/gnome/mutter/src/backends/native/meta-monitor-manager-kms.c: In function 
‘meta_monitor_manager_kms_set_crtc_gamma’:
      ../../../../Source/gnome/mutter/src/backends/native/meta-monitor-manager-kms.c:370:7: warning: 
‘color_char’ may be used uninitialized in this function [-Wmaybe-uninitialized]
        370 |       g_string_append_printf (string, " %c: ", color_char);
            |       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      ../../../../Source/gnome/mutter/src/backends/native/meta-monitor-manager-kms.c:351:12: note: 
‘color_char’ was declared here
        351 |       char color_char;
            |            ^~~~~~~~~~
      ../../../../Source/gnome/mutter/src/backends/native/meta-monitor-manager-kms.c:391:36: warning: 
‘color_ptr’ may be used uninitialized in this function [-Wmaybe-uninitialized]
        391 |                                   (*color_ptr)[i]);
            |                                   ~^~~~~~~~~~~
      ../../../../Source/gnome/mutter/src/backends/native/meta-monitor-manager-kms.c:350:24: note: 
‘color_ptr’ was declared here
        350 |       unsigned short **color_ptr;
            |                        ^~~~~~~~~

 src/backends/native/meta-monitor-manager-kms.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/src/backends/native/meta-monitor-manager-kms.c b/src/backends/native/meta-monitor-manager-kms.c
index b57f98c92f..cc3c2dc4dc 100644
--- a/src/backends/native/meta-monitor-manager-kms.c
+++ b/src/backends/native/meta-monitor-manager-kms.c
@@ -347,7 +347,7 @@ generate_gamma_ramp_string (size_t          size,
   string = g_string_new ("[");
   for (color = 0; color < 3; color++)
     {
-      unsigned short **color_ptr;
+      unsigned short **color_ptr = NULL;
       char color_char;
       size_t i;
 
@@ -367,6 +367,7 @@ generate_gamma_ramp_string (size_t          size,
           break;
         }
 
+      g_assert (color_ptr);
       g_string_append_printf (string, " %c: ", color_char);
       for (i = 0; i < MIN (4, size); i++)
         {