Fixed prev/next fallback order

app/src/main/java/eu/faircode/email/ViewModelMessages.java

@@ -488,12 +488,12 @@ public class ViewModelMessages extends ViewModel {
                             plist.loadAround(pos);
 
                         List<TupleMessageEx> lprev = null;
-                        if (pos - 1 >= 0)
+                        if (pos + 1 < count)
-                            lprev = ds.loadRange(pos - 1, 1);
+                            lprev = ds.loadRange(pos + 1, 1);
 
                         List<TupleMessageEx> lnext = null;
-                        if (pos + 1 < count)
+                        if (pos - 1 >= 0)
-                            lnext = ds.loadRange(pos + 1, 1);
+                            lnext = ds.loadRange(pos - 1, 1);
 
                         TupleMessageEx prev = (lprev != null && lprev.size() > 0 ? lprev.get(0) : null);
                         TupleMessageEx next = (lnext != null && lnext.size() > 0 ? lnext.get(0) : null);