obs-browser: Fix "shutdown when invisible" issue

The browser source would always create the source on first start
regardless of whether "shutdown when not showing" was set or not and the
source wasn't visible.  This fixes the issue by checking whether the
source is actually showing or not in that case.

obs-browser @ bc0745cd

-Subproject commit c5436026ade9c9043230aa995dacb03aa4f1d570
+Subproject commit bc0745cd4bc0b38f7a0a620d053881c123d0f485