mainform: fix the bug where choosing a small size from the menu (typically 1x) would cause unexpected black bars

BizHawk.MultiClient/MainForm.cs

@@ -2686,6 +2686,9 @@ namespace BizHawk.MultiClient
 		}
 
 		public void FrameBufferResized()
+		{
+			// run this entire thing exactly twice, since the first resize may adjust the menu stacking
+			for (int i = 0; i < 2; i++)
 			{
 				var video = Global.Emulator.VideoProvider;
 				int zoom = Global.Config.TargetZoomFactor;
@@ -2716,6 +2719,7 @@ namespace BizHawk.MultiClient
 						Location = new Point(Location.X, area.Bottom - Size.Height);
 				}
 			}
+		}
 
 		private bool InFullscreen = false;
 		private Point WindowedLocation;