fix edge case in quest episode detection

src/QuestScript.cc

@@ -1667,9 +1667,10 @@ Episode find_quest_episode_from_script(const void* data, size_t size, Version ve
       throw logic_error("invalid quest version");
   }
 
-  const auto& opcodes = opcodes_for_version(version);
   unordered_set<Episode> found_episodes;
 
+  try {
+    const auto& opcodes = opcodes_for_version(version);
     // The set_episode opcode should always be in the first function (0)
     StringReader cmd_r = r.sub(code_offset + r.pget_u32l(function_table_offset));
 
@@ -1762,6 +1763,9 @@ Episode find_quest_episode_from_script(const void* data, size_t size, Version ve
         }
       }
     }
+  } catch (const exception& e) {
+    log_warning("Cannot determine episode from quest script (%s)", e.what());
+  }
 
   if (found_episodes.size() > 1) {
     throw runtime_error("multiple episodes found");