fix: fmtstring printing

src/vm/handlers/group_str.c

@@ -1,3 +1,4 @@
+#include <stdio.h>
 #include <string.h>
 #include <vm/fzl_vm.h>
 #include <vm/internals/opcode.h>
@@ -29,7 +30,7 @@ int op_build_str(fzl_vm_t *vm)
     }
 
     memset(temp, 0, sizeof(temp));
-    fzl_value_t val = vm->dstack[i];
+    fzl_value_t val = vm->dstack[vm->dtop - n + i];
 
     switch (val.type)
     {