LibWasm: Make memory_grow validation push back the old memory size

Author: https://github.com/alimpfard
Commit: https://github.com/SerenityOS/serenity/commit/6760ea33a0
Pull-request: https://github.com/SerenityOS/serenity/pull/13770
Reviewed-by: https://github.com/sin-ack ✅

Userland/Libraries/LibWasm/AbstractMachine/Validator.cpp

@@ -1873,6 +1873,7 @@ VALIDATE_INSTRUCTION(memory_grow)
 {
     TRY(validate(MemoryIndex { 0 }));
     TRY((stack.take<ValueType::I32>()));
+    stack.append(ValueType(ValueType::I32));
 
     return {};
 }