fix(runtime-core) Drop vm::FuncCtx if not null.

lib/runtime-core/src/backing.rs

@@ -563,10 +563,12 @@ impl Drop for ImportBacking {
     fn drop(&mut self) {
         // Properly drop the `vm::FuncCtx` in `vm::ImportedFunc`.
         for (_imported_func_index, imported_func) in (*self.vm_functions).iter_mut() {
+            if !imported_func.func_ctx.as_ptr().is_null() {
                 let _: Box<vm::FuncCtx> = unsafe { Box::from_raw(imported_func.func_ctx.as_ptr()) };
             }
         }
     }
+}
 
 fn import_functions(
     module: &ModuleInner,