Ensure that the left of the input window is always visible

The priority of the candidate words in the left of the input window is higher than
those in the right. So it's more intuitive to ensure that the left of the input window
is always visible.

src/ui/classic/xcbinputwindow.cpp

@@ -74,6 +74,8 @@ int XCBInputWindow::calculatePositionX(const Rect &cursorRect,
         if (newX + actualWidth > closestScreen->right()) {
             newX = closestScreen->right() - actualWidth;
         }
+
+        x = std::max(newX, closestScreen->left());
     }
 
     // exclude shadow border width