vbscript: Added support for VT_NULL in stack_pop_bool.

dlls/vbscript/interp.c

@@ -373,6 +373,9 @@ static int stack_pop_bool(exec_ctx_t *ctx, BOOL *b)
     case VT_BOOL:
         *b = V_BOOL(val.v);
         break;
+    case VT_NULL:
+        *b = FALSE;
+        break;
     case VT_I2:
         *b = V_I2(val.v);
         break;

dlls/vbscript/tests/lang.vbs

@@ -434,6 +434,12 @@ do while true
     next
 loop
 
+if null then call ok(false, "if null evaluated")
+
+while null
+    call ok(false, "while null evaluated")
+wend
+
 Call collectionObj.reset()
 y = 0
 x = 10