vout: fix segmentation fault if initialization fails

(cherry picked from commit 97e88867dde80bfd90e4d1c42d08bde34e1314e3)

src/video_output/vout_wrapper.c

@@ -150,6 +150,8 @@ int vout_InitWrapper(vout_thread_t *vout)
             picture_pool_NewFromFormat(&source,
                                        __MAX(VOUT_MAX_PICTURES,
                                              reserved_picture + decoder_picture - DISPLAY_PICTURE_COUNT));
+        if (!sys->decoder_pool)
+            return VLC_EGENERIC;
         if (allow_dr) {
             msg_Warn(vout, "Not enough direct buffers, using system memory");
             sys->dpb_size = 0;