QStandardPaths: remove trailing slash when reading from user-dirs.dirs

For consistency with all other sources of paths, which do not return
a trailing slash, as tested by the unittest. This avoids double slashes
in paths, after apps append something to the path.

Change-Id: Iabcde11eee27df0b185780e2b655fbbb02ed63b5
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/io/qstandardpaths_unix.cpp

@@ -205,6 +205,8 @@ QString QStandardPaths::writableLocation(StandardLocation type)
                 // value can start with $HOME
                 if (value.startsWith(QLatin1String("$HOME")))
                     value = QDir::homePath() + value.mid(5);
+                if (value.length() > 1 && value.endsWith(QLatin1Char('/')))
+                    value.chop(1);
                 return value;
             }
         }