QNX: Don't crash with 0 by 0 sized windows

In the rare event of an invalid sized window, the application crashes
because libscreen doesn't like creating empty buffers.

Not creating the buffers at all would also be a solution, if we didn't
have QPainter crashes due do null paint devices.

Change-Id: I561d0082576b6226dd52129f9640952ba46273c8
Reviewed-by: Kevin Krammer <kevin.krammer@kdab.com>
Reviewed-by: Sean Harmer <sean.harmer@kdab.com>

src/plugins/platforms/qnx/qqnxwindow.cpp

@@ -335,7 +335,11 @@ void QQnxWindow::setBufferSize(const QSize &size)
 
     // Set window buffer size
     errno = 0;
-    int val[2] = { size.width(), size.height() };
+
+    // libscreen fails when creating empty buffers
+    const QSize nonEmptySize = size.isEmpty() ? QSize(1, 1) : size;
+
+    int val[2] = { nonEmptySize.width(), nonEmptySize.height() };
     int result = screen_set_window_property_iv(m_window, SCREEN_PROPERTY_BUFFER_SIZE, val);
     if (result != 0) {
         qFatal("QQnxWindow: failed to set window buffer size, errno=%d", errno);
@@ -381,7 +385,7 @@ void QQnxWindow::setBufferSize(const QSize &size)
     }
 
     // Cache new buffer size
-    m_bufferSize = size;
+    m_bufferSize = nonEmptySize;
 
     // Buffers were destroyed; reacquire them
     m_currentBufferIndex = -1;