Remove strvar_len

The length limit of string variables was removed a long time ago, but it
was recorded in save files.

Now the first argument of MZ0 is completely ignored (as in System3.9).
The maxlen field in the save file is set to a constant so that older
versions of xsystem35 can load it.

src/variable.c

@@ -48,9 +48,7 @@ struct VarPage varPage[PAGE_MAX];
 double longVar[SYSVARLONG_MAX];
 /* 文字列変数 */
 static char **strVar;
-/* 文字列変数の属性(最大,1つあたりの大きさ) */
-int strvar_cnt;
-int strvar_len;
+static int strvar_cnt;
 
 const char *v_name(int var) {
 	if (var < nact->ain.varnum)
@@ -154,7 +152,7 @@ void v_getPageStatus(int page, int *in_use, int *size) {
 }
 
 /* 文字列変数の再初期化 */
-void svar_init(int max_index, int len) {
+void svar_init(int max_index) {
 	for (int i = max_index + 1; i < strvar_cnt; i++) {
 		if (strVar[i])
 			free(strVar[i]);
@@ -166,7 +164,6 @@ void svar_init(int max_index, int len) {
 	for (int i = strvar_cnt; i <= max_index; i++)
 		strVar[i] = NULL;
 	strvar_cnt = max_index + 1;
-	strvar_len = len;
 }
 
 int svar_maxindex(void) {
@@ -178,7 +175,7 @@ void v_init(void) {
 	varPage[0].value = sysVar;
 	varPage[0].size = SYSVAR_MAX;
 	varPage[0].saveflag = true;
-	svar_init(STRVAR_MAX - 1, STRVAR_LEN);
+	svar_init(STRVAR_MAX - 1);
 }
 
 void v_reset(void) {