[PATCH] libdwfl: Do not dlopen libdebuginfod if DEBUGINFOD_URLS is unset or empty

[Frank Ch. Eigler]

Hi -

> [...] The problem with doing the dlopen late is that we also need
> libcurl and initializing libcurl (as done by libdebuginfod) is not
> thread-safe.

>From reading libcurl code, and that of other clients, I still believe
this concern was & is overrated.  We could back down to simple
debuginfod_begin time mutex-protected curl_global_init calls, and we'd
be as fine as other applications.  We could ditch the dlopen /
dso-ctor issues entirely.

- FChE