vout/opengl: module should define capabilities

  This was notably causing a SEGV in the configuration interface.
Signed-off-by: Thomas Guillem <thomas@gllm.fr>

modules/video_output/opengl/vout_helper.h

@@ -61,7 +61,7 @@
 #define GLCONV_TEXT N_("Open GL/GLES hardware converter")
 #define GLCONV_LONGTEXT N_( \
     "Force a \"glconv\" module.")
-#define add_glconv() add_module ("glconv", NULL, NULL, GLCONV_TEXT, GLCONV_LONGTEXT, true)
+#define add_glconv() add_module ("glconv", "glconv", NULL, GLCONV_TEXT, GLCONV_LONGTEXT, true)
 
 static const vlc_fourcc_t gl_subpicture_chromas[] = {
     VLC_CODEC_RGBA,