When invoking a native function as toplevel VM call which indirectly
triggers an unhandled exception in managed code, the callframes are
completely reset before the C function returns, leading to invalid
memory accesses when `uc_vm_call_native()` subsequently popped it's
own callframe again.

This issue did not surface by executing script code through the
interpreter since in this case the VM will always execute a managed
code as toplevel call, but it could be triggered by invoking a native
function triggering an exception through the C API using `uc_vm_call()`
on a fresh `uc_vm_t` context or by utilizing the CLI interpreters `-l`
flag to preload a native code library triggering an exception.


-- File ex.uc --
die("Exception");
-- End --

-- Args --
-L files/ -l ex
-- End --

-- Expect stderr --
Exception
In main(), file files/ex.uc, line 1, byte 16:
  called from anonymous function ([C])

 `die("Exception");`
  Near here -----^


-- End --

-- Testcase --
not reached
-- End --