[Stack Switching] Trap on cont.bind of a null continuation (#8477)

Before this we asserted.

Author: kripken

src/wasm-interpreter.h

@@ -4770,9 +4770,14 @@ class ModuleRunnerBase : public ExpressionRunner<SubType> {
     VISIT_ARGUMENTS(flow, curr->operands, arguments)
     VISIT(cont, curr->cont)
 
+    auto contValue = cont.getSingleValue();
+    if (contValue.isNull()) {
+      trap("null ref");
+    }
+
     // Create a new continuation, copying the old but with the new type +
     // arguments.
-    auto old = cont.getSingleValue().getContData();
+    auto old = contValue.getContData();
     auto newData = *old;
     newData.type = curr->type.getHeapType();
     for (auto arg : arguments) {

test/lit/exec/cont_bindings.wast

@@ -43,5 +43,16 @@
    )
   )
  )
+
+ ;; CHECK:      [fuzz-exec] calling null-binding
+ ;; CHECK-NEXT: [trap null ref]
+ (func $null-binding (export "null-binding")
+  (drop
+   (cont.bind $C1 $C2
+    (i32.const 42)
+    (ref.null $C1)
+   )
+  )
+ )
 )