image-source: Have images not unload by default

Images continually loading/unloading every time transitioning occurs
adds a lot of unnecessary transition lag.  The user can always change
this value manually and/or use scene collections, so change the default
setting to make it not unload/reload by default feels a bit more safe.

plugins/image-source/image-source.c

@@ -100,7 +100,7 @@ static void image_source_update(void *data, obs_data_t *settings)
 
 static void image_source_defaults(obs_data_t *settings)
 {
-	obs_data_set_default_bool(settings, "unload", true);
+	obs_data_set_default_bool(settings, "unload", false);
 }
 
 static void image_source_show(void *data)