Don't call exit(), but return nullptr.

DownloadDCJsonFiles/update.cpp

@@ -46,7 +46,7 @@ hwinf *Update::loadDCPlugin(QDir const &plugInDir, QString const &fname) {
                 qCritical() << "in directory" << plugInDir.absolutePath();
                 qCritical() << "cannot load plugin" << pluginLoader.fileName();
                 qCritical() << pluginLoader.errorString();
-                exit(-1);
+                return nullptr;
             }
 
             qCritical() << "loadDCPlugin() plugin directory:" << plugInDir.absolutePath();
@@ -54,25 +54,25 @@ hwinf *Update::loadDCPlugin(QDir const &plugInDir, QString const &fname) {
 
             if (!pluginLoader.isLoaded()) {
                 qCritical() << pluginLoader.errorString();
-                exit(-2);
+                return nullptr;
             }
             QObject *plugin = pluginLoader.instance();
             if (!plugin) {
                 qCritical() << "cannot start instance";
-                exit(-3);
+                return nullptr;
             }
             if (! (hw = qobject_cast<hwinf *>(plugin))) {
                 qCritical() << "cannot cast plugin" << plugin << "to hwinf";
-                exit(-4);
+                return nullptr;
             }
         } else {
             qCritical() << pluginLibName << "does not exist";
-            exit(-5);
+            return nullptr;
         }
     } else {
         qCritical() << "plugins directory" << plugInDir.absolutePath()
                     << "does not exist";
-        exit(-6);
+        return nullptr;
     }
     return hw;
 }