core/movie: Add future event and timeline check

As specified in TASVideos [Laws of TAS](http://tasvideos.org/LawsOfTAS/OnSavestates.html)

src/core/movie.cpp

@@ -2,6 +2,7 @@
 // Licensed under GPLv2 or any later version
 // Refer to the license.txt file included.
 
+#include <algorithm>
 #include <cstring>
 #include <stdexcept>
 #include <string>
@@ -182,10 +183,16 @@ void Movie::serialize(Archive& ar, const unsigned int file_version) {
             if (play_mode == PlayMode::Recording) {
                 SaveMovie();
             }
-            if (current_byte >= recorded_input.size()) {
+            if (recorded_input_.size() >= recorded_input.size()) {
-                throw std::runtime_error(
+                throw std::runtime_error("Future event savestate not allowed in R/O mode");
-                    "This savestate was created at a later point and must be loaded in R+W mode");
             }
+            // Ensure that the current movie and savestate movie are in the same timeline
+            if (std::mismatch(recorded_input_.begin(), recorded_input_.end(),
+                              recorded_input.begin())
+                    .first != recorded_input_.end()) {
+                throw std::runtime_error("Timeline mismatch not allowed in R/O mode");
+            }
+
             play_mode = PlayMode::Playing;
             total_input = GetInputCount(recorded_input);
         } else {