Fix segmentation fault caused by findMatchedDelim unsafe NULL pointer

[ddelemeny]

built on current master.

In the code editor, trying to highlight a matching delimiter in the following code will cause segmentation fault.

func())))))

findMatchedDelim may return NULL, which should instantaneously break out of the loop and avoid dereferencing a NULL pointer when checking for the loop condition.

Also, the current pointer should probably be bound by TIC_CODE_SIZE (it currently isn't and looks like it can go outside of the code memory segment).

[nesbox]

thanks