Merge #498: tests: Avoid calling fclose(...) with an invalid argument

5aae5b5 Avoid calling fclose(...) with an invalid argument (practicalswift)

Pull request description:

  Avoid calling `fclose(...)` with an invalid argument.

Tree-SHA512: f1a057b8c52089a3af1d9bfe97b751a4003b944d293147855eca452d1766c4ead5701d06f546153e654c9cb07b3fe2bcc4e28c8a54a27263d1e2434be123ca3b

src/tests.c

@@ -4929,7 +4929,9 @@ int main(int argc, char **argv) {
             seed16[6] ^= t >> 48;
             seed16[7] ^= t >> 56;
         }
-        fclose(frand);
+        if (frand) {
+            fclose(frand);
+        }
     }
     secp256k1_rand_seed(seed16);