Fix the issues in git__on_shutdown

src/global.c

@@ -23,7 +23,7 @@ static git_atomic git__n_inits;
 void git__on_shutdown(git_global_shutdown_fn callback)
 {
 	int count = git_atomic_inc(&git__n_shutdown_callbacks);
-	assert(count <= MAX_SHUTDOWN_CB);
+	assert(count <= MAX_SHUTDOWN_CB && count > 0);
 	git__shutdown_callbacks[count - 1] = callback;
 }
 
@@ -31,10 +31,12 @@ static void git__shutdown(void)
 {
 	int pos;
 
-	while ((pos = git_atomic_dec(&git__n_shutdown_callbacks)) >= 0) {
-		if (git__shutdown_callbacks[pos])
-			git__shutdown_callbacks[pos]();
-	}
+	for (pos = git_atomic_get(&git__n_shutdown_callbacks); pos > 0; pos = git_atomic_dec(&git__n_shutdown_callbacks))
+		if (git__shutdown_callbacks[pos - 1]) {
+			git__shutdown_callbacks[pos - 1]();
+			git__shutdown_callbacks[pos - 1] = NULL;
+		}
+
 }
 
 /**

src/sysdir.c

@@ -90,6 +90,8 @@ void git_sysdir_global_shutdown(void)
 	int i;
 	for (i = 0; i < GIT_SYSDIR__MAX; ++i)
 		git_buf_free(&git_sysdir__dirs[i]);
+
+	git_sysdir__dirs_shutdown_set = 0;
 }
 
 static int git_sysdir_check_selector(git_sysdir_t which)