Use overriden resume for co_await on tasklet

Issue here is that if mixed-mode resumption ends up in use,
then a deferred resume can "continue" after a co_await
immediate resume, and then the coroutine handle used
for the deferred resume is dangling.

sigslot/tasklet.h

@@ -8,6 +8,7 @@
 #include <sigslot/sigslot.h>
 #include <coroutine>
 #include <string>
+#include <stdexcept>
 
 namespace sigslot {
     template<typename T> struct tasklet;
@@ -103,7 +104,7 @@ namespace sigslot {
 
             void resolve() {
                 resolved = true;
-                if (awaiting) awaiting.resume();
+                if (awaiting) resume(awaiting);
             }
 
             virtual ~awaitable_base() = default;