Don't use pathJoin for URLs

Problem happens only on Windows that uses \ for path separators and only when primary download location does not contain requested file with requested checksum.

To repro, it should be enough to change one checksum in resources.xml

Report from Manatauro:

![pathjoin](/uploads/4b969168ba7babc21108c1db1a680f66/pathjoin.jpg)

****
mana/plus!82

1 files changed, 1 insertions, 2 deletions

diff --git a/src/gui/windows/updaterwindow.cpp b/src/gui/windows/updaterwindow.cpp
index 948ce5a17..2ed01f4f3 100644
--- a/src/gui/windows/updaterwindow.cpp
+++ b/src/gui/windows/updaterwindow.cpp
@@ -619,8 +619,7 @@ void UpdaterWindow::download()
             const STD_VECTOR<std::string> &mirrors = settings.updateMirrors;
             FOR_EACH (STD_VECTOR<std::string>::const_iterator, it, mirrors)
             {
-                mDownload->addMirror(pathJoin(*it,
-                    mCurrentFile));
+                mDownload->addMirror(urlJoin(*it, mCurrentFile));
             }
         }
     }