Fix few wasm-c-api python binding issues (#2029)

How to python language binding test cases:
```
$ cd <wamr_dir>/language-bindings/python
$ python -m pip install -e .
$ cd wasm-c-api
$ python -m unittest tests/test_basic.py
$ python -m unittest tests/test_advanced.py
```

core/iwasm/common/wasm_c_api.c

@@ -1905,7 +1905,7 @@ wasm_trap_new_internal(wasm_store_t *store,
     }
 
     /* fill in message */
-    if (strlen(error_info) > 0) {
+    if (error_info && strlen(error_info) > 0) {
         if (!(trap->message = malloc_internal(sizeof(wasm_byte_vec_t)))) {
             goto failed;
         }