clients: Implement minimum size for toy toolkit clients

We default to setting the minimum size to the initial size.  To set a
different minimum size than the initial size, set the minimum size first
then then initial size.  Good enough for a toy toolkit.

https://bugs.freedesktop.org/show_bug.cgi?id=50263

clients/terminal.c

@@ -695,10 +695,6 @@ terminal_resize_cells(struct terminal *terminal, int width, int height)
 	struct rectangle allocation;
 	struct winsize ws;
 
-	if (width < 1)
-		width = 1;
-	if (height < 1)
-		height = 1;
 	if (terminal->width == width && terminal->height == height)
 		return;
 
@@ -764,12 +760,6 @@ resize_handler(struct widget *widget,
 	struct terminal *terminal = data;
 	int32_t columns, rows, m;
 
-    if (width < 200)
-        width = 200;
-
-    if (height < 50)
-        height = 50;
-
 	m = 2 * terminal->margin;
 	columns = (width - m) / (int32_t) terminal->extents.max_x_advance;
 	rows = (height - m) / (int32_t) terminal->extents.height;
@@ -2492,6 +2482,7 @@ terminal_create(struct display *display, int fullscreen)
 	cairo_destroy(cr);
 	cairo_surface_destroy(surface);
 
+	terminal_resize(terminal, 20, 5); /* Set minimum size first */
 	terminal_resize(terminal, 80, 25);
 
 	wl_list_insert(terminal_list.prev, &terminal->link);

clients/window.c

@@ -135,6 +135,7 @@ struct window {
 	struct wl_region *opaque_region;
 	char *title;
 	struct rectangle allocation, saved_allocation, server_allocation;
+	struct rectangle min_allocation;
 	struct rectangle pending_allocation;
 	int x, y;
 	int resize_edges;
@@ -2614,6 +2615,13 @@ window_schedule_resize(struct window *window, int width, int height)
 	window->pending_allocation.width = width;
 	window->pending_allocation.height = height;
 
+	if (window->min_allocation.width == 0)
+		window->min_allocation = window->pending_allocation;
+	if (window->pending_allocation.width < window->min_allocation.width)
+		window->pending_allocation.width = window->min_allocation.width;
+	if (window->pending_allocation.height < window->min_allocation.height)
+		window->pending_allocation.height = window->min_allocation.height;
+
 	window->resize_needed = 1;
 	window_schedule_redraw(window);
 }