Fix sql wrong file name. Fix can not save email settings bug.

src/main/kotlin/top/fatweb/api/settings/SettingsOperator.kt

@@ -91,11 +91,8 @@ object SettingsOperator {
                 }
             }
             field.set(it, value)
-        } ?: {
+        } ?: let {
-            MailSettings().also {
+            systemSettings.mail = MailSettings().also { field.set(it, value) }
-                field.set(it, value)
-                systemSettings.mail = it
-            }
         }
 
         saveSettingsToFile()