Derive default patchEC value from scenario signature

The EC bug exists only in System 3.8 and later. System 3.5 / 3.6 games
(e.g. Atlach=Nacha) need the patched behavior.

This deviates from System39.exe, which has the buggy behavior for older
scenarios too.

src/nact.c

@@ -167,7 +167,9 @@ void nact_init() {
 
 	sel_init();
 
-	nact->patch_ec = false;
+	// The EC bug was introduced in System 3.8. Older games expect the
+	// patch_ec=true behavior.
+	nact->patch_ec = !sl_is_s380;
 	nact->patch_emen = false;
 	nact->patch_g0 = false;
 

src/scenario.c

@@ -36,6 +36,7 @@
 const uint8_t *sl_sco;
 int sl_page;
 int sl_index;
+bool sl_is_s380;
 
 static void pop_state(uint8_t tag);
 
@@ -102,6 +103,7 @@ bool sl_init(void) {
 	
 	stack_top = stack_buf;
 	sl_jmpFar(0);
+	sl_is_s380 = !memcmp(sl_sco, "S380", 4);
 
 	return true;
 }

src/scenario.h

@@ -54,6 +54,8 @@ struct stack_frame_info {
 	uint8_t *p;     // for internal use
 };
 
+extern bool sl_is_s380;
+
 // Use functions below instead of accessing these variables directly.
 extern const uint8_t *sl_sco; // scenario page buffer
 extern int sl_page;        // current scenario page (0-based)

src/xsystem35.c

@@ -147,10 +147,10 @@ static void sys35_usage(bool verbose) {
 static void sys35_init() {
 	int i;
 	
-	nact_init();
-	
 	sl_init();
 
+	nact_init();
+
 	v_init();
 	
 	ags_init(render_driver, enable_zb);