Make sure x input window is with in screen after Flip Y.

In certian cases, the flip y may move window out of screen. We should
move the window back with slide y logic.

src/ui/classic/xcbinputwindow.cpp

@@ -75,31 +75,40 @@ void XCBInputWindow::updatePosition(InputContext *inputContext) {
     }
 
     if (closestScreen) {
-        int newX, newY;
+        int newX;
 
         if (x < closestScreen->left()) {
             newX = closestScreen->left();
         } else {
             newX = x;
         }
 
+        if ((newX + static_cast<int>(actualWidth)) > closestScreen->right()) {
+            newX = closestScreen->right() - actualWidth;
+        }
+
+        int newY;
         if (y < closestScreen->top()) {
             newY = closestScreen->top();
         } else {
             newY = y + (h ? h : (10 * ((dpi_ < 0 ? 96.0 : dpi_) / 96.0)));
         }
 
-        if ((newX + static_cast<int>(actualWidth)) > closestScreen->right()) {
-            newX = closestScreen->right() - actualWidth;
-        }
-
+        // Try flip y.
         if ((newY + static_cast<int>(actualHeight)) > closestScreen->bottom()) {
             if (newY > closestScreen->bottom()) {
                 newY = closestScreen->bottom() - actualHeight - 40;
             } else { /* better position the window */
                 newY = newY - actualHeight - ((h == 0) ? 40 : h);
             }
+
+            // If after flip, top is out of the screen, we still prefer the top
+            // edge to be always with in screen.
+            if (newY < closestScreen->top()) {
+                newY = closestScreen->top();
+            }
         }
+
         x = newX;
         y = newY;
     }