Merge pull request #6 from 0dminnimda/foolproof-init-and-finish

Foolproof coroutine_init and coroutine_finish

Author: rexim

coroutine.c

@@ -200,12 +200,14 @@ void coroutine_switch_context(void *rsp, Sleep_Mode sm, int fd)
 
 void coroutine_init(void)
 {
+    if (contexts.count != 0) return;
     da_append(&contexts, (Context){0});
     da_append(&active, 0);
 }
 
 void coroutine_finish(void)
 {
+    if (contexts.count == 0) return;
     if (active.items[current] == 0) {
         for (size_t i = 1; i < contexts.count; ++i) {
             munmap(contexts.items[i].stack_base, STACK_CAPACITY);