fix a few bugs in model loading

Each time `model_load` is called with a `ship_info` pointer, which causes it to load subsystems, the model number MUST be assigned to the ship_info.

Author: Goober5000

code/mission/missionparse.cpp

@@ -5347,6 +5347,7 @@ void resolve_path_masks(bool path_user_is_ship, const char *path_user, anchor_t
 		// Load the anchor ship model with subsystems and all; it'll need to be done for this mission anyway
 		auto anchor_sip = anchor_ship_entry->sip();
 		modelnum = model_load(anchor_sip->pof_file, anchor_sip);
+		anchor_sip->model_num = modelnum;
 
 		// resolve names to indexes
 		*path_mask = 0;
@@ -7075,6 +7076,7 @@ bool post_process_mission(mission *pm)
 				if (valid) {
 					ship_info* sip = &Ship_info[icon.ship_class];
 					stage.icons[j].modelnum = model_load(sip->pof_file, sip);
+					sip->model_num = stage.icons[j].modelnum;
 				}
 			}
 		}
@@ -8944,6 +8946,7 @@ void check_anchor_for_hangar_bay(SCP_string &message, SCP_set<anchor_t> &anchors
 		// Load the anchor ship model with subsystems and all; it'll need to be done for this mission anyway
 		auto anchor_sip = anchor_ship_entry->sip();
 		int modelnum = model_load(anchor_sip->pof_file, anchor_sip);
+		anchor_sip->model_num = modelnum;
 
 		// Check if this model has a hangar bay
 		if (!model_has_hangar_bay(modelnum))

code/model/model.h

@@ -1005,9 +1005,11 @@ void model_free_all();
 void model_instance_free_all();
 
 // Alias to model_load, checks if a pof tech model exists and loads it if specified, otherwise loads the default pof. --wookieejedi
+// NOTE: Each time model_load is called with a ship_info pointer, which causes it to load subsystems, the model number MUST be assigned to the ship_info.
 int model_load(ship_info* sip, bool prefer_tech_model);
 
 // Loads a model from disk and returns the model number it loaded into.
+// NOTE: Each time model_load is called with a ship_info pointer, which causes it to load subsystems, the model number MUST be assigned to the ship_info.
 int model_load(const char *filename, ship_info* sip = nullptr, ErrorType error_type = ErrorType::FATAL_ERROR, bool allow_redundant_load = false);
 
 int model_create_instance(int objnum, int model_num);