Dont print to stderr from _set_error if iscsi is NULL

If iscsi is NULL then just do nothing and dont log to stderr.
Our caller might have closed stderr or worse, re-used fd 2 for something else.

lib/init.c

@@ -255,9 +255,6 @@ iscsi_set_error(struct iscsi_context *iscsi, const char *error_string, ...)
 		strncpy(iscsi->error_string,errstr,MAX_STRING_SIZE);
 		DPRINTF(iscsi,1,"%s",iscsi->error_string);
 	}
-	else {
-		fprintf(stderr,"libiscsi: %s\n", errstr);
-	}
 }
 
 void