system.ExistFile() should return false if path ends with a backslash

The system.ExistsFile() system call returns 1 if a file or directory
exists, but returns 0 when the provided path ends with a directory
separator, regardless of whether a directory exists at that location.

This subtle difference in behavior caused problems in Pastel Chime 3.

src/vm.c

@@ -559,7 +559,13 @@ static void system_call(enum syscall_code code)
 	case SYS_EXISTS_FILE: { // system.ExistsFile(string szFileName)
 		int str = stack_pop().i;
 		char *path = gamedir_path(heap_get_string(str)->text);
-		stack_push(file_exists(path));
+		int len = strlen(path);
+		// Return true for directories, but false if the path ends with a directory separator.
+		if (len > 0 && (path[len-1] == '/' || path[len-1] == '\\')) {
+			stack_push(0);
+		} else {
+			stack_push(file_exists(path));
+		}
 		heap_unref(str);
 		free(path);
 		break;

test/Source/main.jaf

@@ -84,6 +84,10 @@ int main(void)
 	test_arrays();
 	test_end("arrays");
 
+	test_start("system");
+	test_system();
+	test_end("system");
+
 	test_start("Math.dll");
 	test_math();
 	test_end("Math.dll");

test/Source/system.jaf

@@ -0,0 +1,8 @@
+// -*-mode: C; coding: sjis; -*-
+
+void test_system(void)
+{
+	string savedir = system.GetSaveFolderName();
+	test_equal("system.ExistFile(savedir) == 1", system.ExistFile(savedir), 1);
+	test_equal("system.ExistFile(savedir + \"\\\\\") == 1", system.ExistFile(savedir + "\\"), 0);
+}

test/Source/test.inc

@@ -4,6 +4,7 @@ Source = {
 "arithmetic.jaf",
 "strings.jaf",
 "structs.jaf",
+"system.jaf",
 "arrays.jaf",
 "math.jaf"
 }