wined3d: Avoid WARN() when failing to allocate a GL BO without a context.

dlls/wined3d/adapter_gl.c

@@ -4657,7 +4657,6 @@ static bool adapter_gl_alloc_bo(struct wined3d_device *device, struct wined3d_re
 
     if (!(wined3d_device_gl_create_bo(device_gl, NULL, size, binding, usage, coherent, flags, bo_gl)))
     {
-        WARN("Failed to create OpenGL buffer.\n");
         heap_free(bo_gl);
         return false;
     }

dlls/wined3d/device.c

@@ -1130,6 +1130,8 @@ bool wined3d_device_gl_create_bo(struct wined3d_device_gl *device_gl, struct win
         {
             if ((memory = wined3d_device_gl_allocate_memory(device_gl, context_gl, memory_type_idx, size, &id)))
                 buffer_offset = memory->offset;
+            else if (!context_gl)
+                WARN_(d3d_perf)("Failed to suballocate buffer from the client thread.\n");
         }
         else if (context_gl)
         {
@@ -1139,7 +1141,8 @@ bool wined3d_device_gl_create_bo(struct wined3d_device_gl *device_gl, struct win
 
         if (!id)
         {
-            WARN("Failed to allocate buffer.\n");
+            if (context_gl)
+                WARN("Failed to allocate buffer.\n");
             return false;
         }
     }