Fix refreshing PatchScreen when fileList has not yet been loaded

Although PatchScreen and PatchTable typically guard against using a
not yet loaded PatchTable, refreshing a PatchScreen and the subsequent
moving of the pointer lacked such guards. Thereby, a race condition
was introduced that lead to issue 1749.
We now added guards in both PatchScreen, and PatchTable.

Bug: issue 1749
Change-Id: I03ee3e80c198373ebecc50b1135b9c542d8ecfe7
(cherry picked from commit da5ceb4c9c73306b90be4349a4e7e106ab78e676)