Remove some checks leading to default values

Large TreeSheets window on a secondary screen satisifes
`posx + resx > disprect.width + disprect.x` on X11
because `disprect` only refers to the primary screen.

Example:
```
(gdb) p posx
$6 = 2688
(gdb) p resx
$7 = 2432
(gdb) p disprect.width
$8 = 2560
(gdb) p disprect.x
$9 = 0
```

src/myframe.h

@@ -696,8 +696,13 @@ struct MyFrame : wxFrame {
         sys->cfg->Read(L"posx", &posx, boundary + disprect.x);
         sys->cfg->Read(L"posy", &posy, boundary + disprect.y);
         if (resx > disprect.width || resy > disprect.height || posx < disprect.x ||
-            posy < disprect.y || posx + resx > disprect.width + disprect.x ||
-            posy + resy > disprect.height + disprect.y) {
+            posy < disprect.y
+            #ifndef __WXGTK__
+                // On X11 platforms, disprect only refers to the primary screen
+                || posx + resx > disprect.width + disprect.x
+                || posy + resy > disprect.height + disprect.y
+            #endif
+            ) {
             // Screen res has been resized since we last ran, set sizes to default to avoid being
             // off-screen.
             resx = defx;