Handle missing model in CLI parameters for llama-run (#11399)

The HTTP client in llama-run only prints an error in case the download of
a resource failed. If the model name in the CLI parameter list is missing,
this causes the application to crash.
In order to prevent this, a check for the required model parameter has been
added and errors for resource downloads get propagated to the caller.

Signed-off-by: Michael Engel <mengel@redhat.com>

examples/run/run.cpp

@@ -181,6 +181,10 @@ class Opt {
             }
         }
 
+        if (model_.empty()){
+            return 1;
+        }
+
         return 0;
     }
 
@@ -350,7 +354,11 @@ class HttpClient {
         data.file_size = set_resume_point(output_file_partial);
         set_progress_options(progress, data);
         set_headers(headers);
-        perform(url);
+        CURLcode res = perform(url);
+        if (res != CURLE_OK){
+            printe("Fetching resource '%s' failed: %s\n", url.c_str(), curl_easy_strerror(res));
+            return 1;
+        }
         if (!output_file.empty()) {
             std::filesystem::rename(output_file_partial, output_file);
         }
@@ -415,16 +423,12 @@ class HttpClient {
         }
     }
 
-    void perform(const std::string & url) {
-        CURLcode res;
+    CURLcode perform(const std::string & url) {
         curl_easy_setopt(curl, CURLOPT_URL, url.c_str());
         curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1L);
         curl_easy_setopt(curl, CURLOPT_DEFAULT_PROTOCOL, "https");
         curl_easy_setopt(curl, CURLOPT_FAILONERROR, 1L);
-        res = curl_easy_perform(curl);
-        if (res != CURLE_OK) {
-            printe("curl_easy_perform() failed: %s\n", curl_easy_strerror(res));
-        }
+        return curl_easy_perform(curl);
     }
 
     static std::string human_readable_time(double seconds) {