stdio: fix %N.Ms miscalculating spacing if M > strlen(arg)

src/stdio/printf/format_usual.c

@@ -59,6 +59,8 @@ void __printf_format_s(
 	size_t len = 0;
 	uint32_t precision = opt->precision ? opt->precision : (-1);
 	while(s[len] && len < precision) len++;
+	/* Cap precision to real value for __printf_compute_geometry() */
+	opt->precision = len;
 
 	struct __printf_geometry g = {
 		.prefix = 0, .sign = 0, .content = len,