Honour the minimum size for a container.

Some containers require a minimum size when they draw on their own
canvas.

The change is part 1/2 of the fix for bug #22144.

src/gui/widgets/container.cpp

@@ -94,16 +94,24 @@ tpoint tcontainer_::calculate_best_size() const
 
 	tpoint result(grid_.get_best_size());
 	const tpoint border_size = border_space();
+	const tpoint minimum_size = get_config_minimum_size();
 
 	// If the best size has a value of 0 it's means no limit so don't
 	// add the border_size might set a very small best size.
 	if(result.x) {
 		result.x += border_size.x;
 	}
+	if(minimum_size.x != 0 && result.x < minimum_size.x) {
+		result.x = minimum_size.x;
+	}
 
 	if(result.y) {
 		result.y += border_size.y;
 	}
+	if(minimum_size.y != 0 && result.y < minimum_size.y) {
+		result.y = minimum_size.y;
+	}
+
 
 	DBG_GUI_L << LOG_HEADER << " border size " << border_size << " returning "
 			  << result << ".\n";