src/egl_gbm_render_surface: properly fallback to surface with no modifier

In 869fa7f, we added a fallback to be able to create an EGL sruface
when the driver do not support modifiers, like the llvmpipe software
renderer (or like some proprietary drivers, like the MALI ones), as
reported in #269 [0].

However, in c653767, there was a big overhaul of renderer
infrastructure. That commit lost the with-modifiers code path and only
kept the without-modifiers fallback one (i.e. it only kept the call to
gbm_surface_create(), not to gbm_surface_create_with_modifiers()).

Then in b0d09f5, the with-modifier code path was re-instated, but
in a way that made it exclusive with the without-modifiers one. That is,
the without-modifiers code path was not a fallback to when the other
failed.

Re-instate the fallback mechanism as initially implemented.

[0] #269

Signed-off-by: Yann E. MORIN <[email protected]>

Author: yann-morin-1998

src/egl_gbm_render_surface.c

@@ -146,6 +146,7 @@ static int egl_gbm_render_surface_init(
     }
 #endif
 
+    gbm_surface = NULL;
     if (allowed_modifiers != NULL) {
         gbm_surface = gbm_surface_create_with_modifiers(
             gbm_device,
@@ -158,9 +159,10 @@ static int egl_gbm_render_surface_init(
         if (gbm_surface == NULL) {
             ok = errno;
             LOG_ERROR("Couldn't create GBM surface for rendering. gbm_surface_create_with_modifiers: %s\n", strerror(ok));
-            return ok;
+            LOG_ERROR("Will retry without modifiers\n");
         }
-    } else {
+    }
+    if (gbm_surface == NULL) {
         gbm_surface = gbm_surface_create(
             gbm_device,
             size.x,