libplacebo: opengl: fix double-release

glReleaseCurrent accidentally gets run twice in this code, including
once before creating the swapchain (where we definitely want the process
to be current!).

Fix this logic to only release the context once.

modules/video_output/libplacebo/instance_opengl.c

@@ -121,7 +121,6 @@ static int InitInstance(vlc_placebo_t *pl, const vout_display_cfg_t *cfg)
         .proc_ctx = sys->gl,
 #endif
     });
-    vlc_gl_ReleaseCurrent (sys->gl);
     if (!sys->opengl)
         goto error;
 
@@ -138,6 +137,7 @@ static int InitInstance(vlc_placebo_t *pl, const vout_display_cfg_t *cfg)
         goto error;
 
     vlc_gl_ReleaseCurrent(sys->gl);
+    current = false;
 
     pl->gpu = sys->opengl->gpu;
     pl->ops = &instance_opts;