[agroal#426] Fix a problem in pgagroal_bind

If the configuration `host` is set to `*`, meaning all the interfaces,
the `pgagroal_bind` function was always returning a true value even if
no available bind addresses were left.
In order to fix this, the commit tests if the `star_length` variable
has been set to something non-zero, otherwise no more sockets are
available (bound) and the function returns a `1` to indicate an error.

Close agroal#426

src/libpgagroal/network.c

@@ -121,10 +121,17 @@ pgagroal_bind(const char* hostname, int port, int** fds, int* length, bool non_b
          }
       }
 
+      freeifaddrs(ifaddr);
+
+      if (star_length == 0)
+      {
+         // cannot bind to anything!
+         return 1;
+      }
+
       *fds = star_fds;
       *length = star_length;
 
-      freeifaddrs(ifaddr);
       return 0;
    }