Fix #12133: [Script] Don't crash when emergency saving (#12138)

(cherry picked from commit 25d1238907)

src/ai/ai_core.cpp

@@ -283,14 +283,18 @@
 {
 	if (!_networking || _network_server) {
 		Company *c = Company::GetIfValid(company);
-		assert(c != nullptr && c->ai_instance != nullptr);
-
-		Backup<CompanyID> cur_company(_current_company, company, FILE_LINE);
-		c->ai_instance->Save();
-		cur_company.Restore();
-	} else {
-		AIInstance::SaveEmpty();
+		assert(c != nullptr);
+
+		/* When doing emergency saving, an AI can be not fully initialised. */
+		if (c->ai_instance != nullptr) {
+			Backup<CompanyID> cur_company(_current_company, company, FILE_LINE);
+			c->ai_instance->Save();
+			cur_company.Restore();
+			return;
+		}
 	}
+
+	AIInstance::SaveEmpty();
 }
 
 /* static */ std::string AI::GetConsoleList(bool newest_only)