Remote: Set an error when a remote cannot be found.

Inside `git_remote_load`, the calls to `get_optional_config` use
`giterr_clear` to unset any errors that are set due to missing config
keys. If neither a fetch nor a push url config was found for a remote,
we should set an error again.

src/remote.c

@@ -403,6 +403,7 @@ int git_remote_load(git_remote **out, git_repository *repo, const char *name)
 
 	if (!optional_setting_found) {
 		error = GIT_ENOTFOUND;
+		giterr_set(GITERR_CONFIG, "Remote '%s' does not exist.", name);
 		goto cleanup;
 	}
 

tests/network/remote/remotes.c

@@ -60,6 +60,15 @@ void test_network_remote_remotes__pushurl(void)
 	cl_assert(git_remote_pushurl(_remote) == NULL);
 }
 
+void test_network_remote_remotes__error_when_not_found(void)
+{
+	git_remote *r;
+	cl_git_fail_with(git_remote_load(&r, _repo, "does-not-exist"), GIT_ENOTFOUND);
+
+	cl_assert(giterr_last() != NULL);
+	cl_assert(giterr_last()->klass == GITERR_CONFIG);
+}
+
 void test_network_remote_remotes__error_when_no_push_available(void)
 {
 	git_remote *r;