Merge pull request #3453 from AvaloniaUI/fixes/x11-backend-cope-with-0size-window

Fixes/x11 backend cope with 0size window

src/Avalonia.X11/X11Framebuffer.cs

@@ -14,6 +14,10 @@ namespace Avalonia.X11
 
         public X11Framebuffer(IntPtr display, IntPtr xid, int depth, int width, int height, double factor)
         {
+            // HACK! Please fix renderer, should never ask for 0x0 bitmap.
+            width = Math.Max(1, width);
+            height = Math.Max(1, height);
+
             _display = display;
             _xid = xid;
             _depth = depth;

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

src/Shared/PlatformSupport/StandardRuntimePlatform.cs

@@ -75,7 +75,7 @@ namespace Avalonia.Shared.PlatformSupport
                         lock (_btlock)
                             Backtraces.Remove(_backtrace);
 #endif
-                        _plat.Free(_address, Size);
+                        _plat?.Free(_address, Size);
                         GC.RemoveMemoryPressure(Size);
                         IsDisposed = true;
                         _address = IntPtr.Zero;