Additional sanity checks for monitor resolution

src/Avalonia.X11/X11Window.cs

@@ -102,7 +102,7 @@ namespace Avalonia.X11
                 valueMask |= SetWindowValuemask.ColorMap;   
             }
 
-            int defaultWidth = 300, defaultHeight = 200;
+            int defaultWidth = 0, defaultHeight = 0;
 
             if (!_popup && Screen != null)
             {
@@ -117,6 +117,10 @@ namespace Avalonia.X11
                 }
             }
 
+            // check if the calculated size is zero then compensate to hardcoded resolution
+            defaultWidth = Math.Max(defaultWidth, 300);
+            defaultHeight = Math.Max(defaultHeight, 200);
+
             _handle = XCreateWindow(_x11.Display, _x11.RootWindow, 10, 10, defaultWidth, defaultHeight, 0,
                 depth,
                 (int)CreateWindowArgs.InputOutput, 
@@ -133,7 +137,7 @@ namespace Avalonia.X11
                 _renderHandle = _handle;
                 
             Handle = new PlatformHandle(_handle, "XID");
-            _realSize = new PixelSize(300, 200);
+            _realSize = new PixelSize(defaultWidth, defaultHeight);
             platform.Windows[_handle] = OnEvent;
             XEventMask ignoredMask = XEventMask.SubstructureRedirectMask
                                      | XEventMask.ResizeRedirectMask