Clamp texture view slice to number of slices (sanity checking)

* This should in theory be impossible as you can't create a view that
  points to after the number of slices, and we always make a list of all
  slices, but there was a crash report here so for now we'll just clamp
  so that it doesn't crash completely.

renderdocui/Windows/TextureViewer.cs

@@ -1335,7 +1335,8 @@ namespace renderdocui.Windows
                     }
                 }
 
-                sliceFace.SelectedIndex = (int)m_Following.GetFirstArraySlice(m_Core);
+                int firstArraySlice = (int)m_Following.GetFirstArraySlice(m_Core);
+                sliceFace.SelectedIndex = Helpers.Clamp(firstArraySlice, 0, (int)numSlices - 1);
             }
 
             // mip and slice were reset to 0 above, we must restore any per-tex settings to apply