win-capture: Reset WGC fail flag for new window

WGC will give up on a window that it fails to capture, but that
shouldn't stop it from attempting to capture new windows.

Fixes #2928.

plugins/win-capture/window-capture.c

@@ -421,6 +421,7 @@ static void wc_tick(void *data, float seconds)
 			return;
 		}
 
+		wc->previously_failed = false;
 		reset_capture = true;
 
 	} else if (IsIconic(wc->window)) {