Fix the following warning when chars are unsigned:
viewer.c:988:25: warning: comparison of constant -1 with expression of type 'char' is always true
[-Wtautological-constant-out-of-range-compare]
while((c = getch()) != ERR) {
int get_slide_number(char init) {
int retval = init - '0';
int get_slide_number(char init) {
int retval = init - '0';
// block for tenths of a second when using getch, ERR if no input
halfdelay(GOTO_SLIDE_DELAY);
while((c = getch()) != ERR) {
// block for tenths of a second when using getch, ERR if no input
halfdelay(GOTO_SLIDE_DELAY);
while((c = getch()) != ERR) {