fix(modem): null terminate output buffer if no response in esp_modem_at functions

Author: JellevanKraaij

components/esp_modem/src/esp_modem_c_api.cpp

@@ -217,8 +217,12 @@ extern "C" esp_err_t esp_modem_at(esp_modem_dce_t *dce_wrap, const char *at, cha
     std::string out;
     std::string at_str(at);
     auto ret = command_response_to_esp_err(dce_wrap->dce->at(at_str, out, timeout));
-    if ((p_out != NULL) && (!out.empty())) {
-        strlcpy(p_out, out.c_str(), CONFIG_ESP_MODEM_C_API_STR_MAX);
+    if ((p_out != NULL)) {
+        if (!out.empty()) {
+            strlcpy(p_out, out.c_str(), CONFIG_ESP_MODEM_C_API_STR_MAX);
+        } else {
+            p_out[0] = '\0'; // Clear output buffer if no response
+        }
     }
     return ret;
 }
@@ -251,8 +255,12 @@ extern "C" esp_err_t esp_modem_at_raw(esp_modem_dce_t *dce_wrap, const char *cmd
     }
     std::string out;
     auto ret = command_response_to_esp_err(dce_wrap->dce->at_raw(cmd, out, pass, fail, timeout));
-    if ((p_out != NULL) && (!out.empty())) {
-        strlcpy(p_out, out.c_str(), CONFIG_ESP_MODEM_C_API_STR_MAX);
+    if ((p_out != NULL)) {
+        if (!out.empty()) {
+            strlcpy(p_out, out.c_str(), CONFIG_ESP_MODEM_C_API_STR_MAX);
+        } else {
+            p_out[0] = '\0'; // Clear output buffer if no response
+        }
     }
     return ret;
 }