card: Set initial profile availability state

Commit afd33da56a introduces this new
flag but the default initial value is missing, considering that
pa_xmalloc is used to allocate the memory.

src/pulsecore/card.c

@@ -51,6 +51,7 @@ pa_card_profile *pa_card_profile_new(const char *name, const char *description,
     c->priority = 0;
     c->n_sinks = c->n_sources = 0;
     c->max_sink_channels = c->max_source_channels = 0;
+    c->available = PA_AVAILABLE_UNKNOWN;
 
     return c;
 }