RAND_load_file(): return error if reseeding failed

The failure of RAND_load_file was only noticed because of the
heap corruption which was reported in openssl#7499 and fixed in commit
5b4cb38. To prevent this in the future, RAND_load_file()
now explicitly checks RAND_status() and reports an error if it
fails.

Related-to: openssl#7449

Reviewed-by: Paul Dale <paul.dale@oracle.com>
(Merged from openssl#7456)

crypto/rand/randfile.c

@@ -148,6 +148,12 @@ int RAND_load_file(const char *file, long bytes)
 
     OPENSSL_cleanse(buf, sizeof(buf));
     fclose(in);
+    if (!RAND_status()) {
+        RANDerr(RAND_F_RAND_LOAD_FILE, RAND_R_RESEED_ERROR);
+        ERR_add_error_data(2, "Filename=", file);
+        return -1;
+    }
+
     return ret;
 }