Fix disk space checking to prevent error message

The error message only happens in debug builds, but the cause of
the message still happens in release builds.  Basically, the temporary
project directory may not yet be created if the person is only monitoring.

src/DirManager.cpp

@@ -537,14 +537,21 @@ wxString DirManager::GetProjectName()
 wxLongLong DirManager::GetFreeDiskSpace()
 {
    wxLongLong freeSpace = -1;
-   wxString path = projPath;
+   wxFileName path;
 
-   if (projPath == wxT(""))
-      path = mytemp;
+   path.SetPath(projPath.IsEmpty() ? mytemp : projPath);
+
+   // Use the parent directory if the project directory hasn't yet been created
+   if (!path.DirExists())
    {
-      if (!wxGetDiskSpace(path, NULL, &freeSpace))
-         freeSpace = -1;
+      path.RemoveLastDir();
    }
+
+   if (!wxGetDiskSpace(path.GetFullPath(), NULL, &freeSpace))
+   {
+      freeSpace = -1;
+   }
+
    return freeSpace;
 }