Prevent resizing minimap bigger than GraphEdit (Fix godotengine#47189)

Minimap size couldn't be resized back after been resized bigger than GraphEdit cause the grabber was out of GraphEdit.
This commit prevents resizing minimap bigger than GraphEdit and fix this issue.

(cherry picked from commit 045f55e)

scene/gui/graph_edit.cpp

@@ -181,7 +181,12 @@ void GraphEditMinimap::_gui_input(const Ref<InputEvent> &p_ev) {
 		accept_event();
 	} else if (mm.is_valid() && is_pressing) {
 		if (is_resizing) {
-			ge->set_minimap_size(ge->get_minimap_size() - mm->get_relative());
+			// Prevent setting minimap wider than GraphEdit
+			Vector2 new_minimap_size;
+			new_minimap_size.x = MIN(get_size().x - mm->get_relative().x, ge->get_size().x - 2.0 * minimap_padding.x);
+			new_minimap_size.y = MIN(get_size().y - mm->get_relative().y, ge->get_size().y - 2.0 * minimap_padding.y);
+			ge->set_minimap_size(new_minimap_size);
+
 			update();
 		} else {
 			Vector2 click_position = _convert_to_graph_position(mm->get_position() - minimap_padding) - graph_padding;