client: prevent using and creating proxies after an error occured

We won't receive any response anyway...

This removes the last line of:

[2230782.435] wl_display@1.error(wl_display@1, 2, "no memory")
wl_display@1: error 2: no memory
[2230782.534]  -> wl_display@1.sync(new id wl_callback@3)

and prevents from creating proxy on invalidated display object.
saviour