TT#68300 Do not consider a missing configuration file fatal

We should not consider a missing configuration file a fatal problem,
now that we have defaults for almost every configuration setting,
and can override them at constructor time.

Change-Id: I371498e9d75e81c4c759012ec38b44d050bdea8f

lib/NGCP/API/Client.pm

@@ -16,8 +16,10 @@ sub _load_config_defaults {
     my $cfg_file = '/etc/default/ngcp-api';
     my $cfg;
 
-    $cfg = Config::Tiny->read($cfg_file)
-        or croak("Cannot read $cfg_file: $ERRNO");
+    if (-e $cfg_file) {
+        $cfg = Config::Tiny->read($cfg_file)
+            or croak("Cannot read $cfg_file: $ERRNO");
+    }
 
     Readonly my $config => {
         host          => $cfg->{_}->{NGCP_API_IP} // '127.0.0.1',