Fixed a problem where not supplying the tempdir option could cause a non-default value to be used.

Duplicati/Library/Main/Interface.cs

@@ -2075,7 +2075,7 @@ namespace Duplicati.Library.Main
                 stats.VerboseRetryErrors = m_options.VerboseRetryErrors;
             }
 
-            if (!string.IsNullOrEmpty(m_options.TempDir))
+            if (m_options.HasTempDir)
                 Utility.TempFolder.SystemTempPath = m_options.TempDir;
 
             if (!string.IsNullOrEmpty(m_options.ThreadPriority))

Duplicati/Library/Main/Options.cs

@@ -651,6 +651,11 @@ namespace Duplicati.Library.Main
         /// </summary>
         public bool Force { get { return GetBool("force"); } }
 
+        /// <summary>
+        /// Gets a value indicating whether a temporary folder has been specified
+        /// </summary>
+        public bool HasTempDir { get { return m_options.ContainsKey("tempdir") && !string.IsNullOrEmpty(m_options["tempdir"]); } }
+
         /// <summary>
         /// Gets the folder where temporary files are stored
         /// </summary>