fix writing of the error message to stderr by processing the varargs

--- a/src/error.c
+++ b/src/error.c
@@ -23,7 +23,6 @@ void error_init(error_t *err, int error_code, const char *desc_fmt, ...)
 {
     va_list args;
 
-    fprintf(stderr, "error_init: %d %s", error_code, desc_fmt);
     daemon_assert(err != NULL);
     daemon_assert(error_code >= 0);
     daemon_assert(desc_fmt != NULL);
@@ -32,6 +31,7 @@ void error_init(error_t *err, int error_code, const char *desc_fmt, ...)
     va_start(args, desc_fmt);
     vsnprintf(err->desc, sizeof(err->desc), desc_fmt, args);
     va_end(args);
+    fprintf(stderr, "error_init: %d %s\n", error_code, err->desc);
 
     daemon_assert(invariant(err));
 }