Ignore all control characters not handled

Taken from vt100 programmer manual:

	Control characters have values of \000 - \037, and \177. The control
	characters recognized by the VT100 are shown in Table 3-10. All
	other control codes cause no action to be taken.

We have to take attention when we are using alternate charset, because in
this cases they are not used as control characters.
---
 st.c |   20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

st.c

@@ -1663,7 +1663,7 @@ tputtab(bool forward) {
 
 void
 tputc(char *c, int len) {
-	char ascii = *c;
+	uchar ascii = *c;
 
 	if(iofd != -1)
 		write(iofd, c, len);
@@ -1792,8 +1792,6 @@ tputc(char *c, int len) {
 		if(sel.bx != -1 && BETWEEN(term.c.y, sel.by, sel.ey))
 			sel.bx = -1;
 		switch(ascii) {
-		case '\0': /* padding character, do nothing */
-			break;
 		case '\t':
 			tputtab(1);
 			break;
@@ -1818,6 +1816,7 @@ tputc(char *c, int len) {
 			term.esc = ESC_START;
 			break;
 		default:
+			if(ascii >= '\020' || term.c.attr.mode & ATTR_GFX) {
 				if(IS_SET(MODE_WRAP) && term.c.state & CURSOR_WRAPNEXT)
 					tnewline(1); /* always go to first col */
 				tsetchar(c);
@@ -1828,6 +1827,7 @@ tputc(char *c, int len) {
 			}
 		}
 	}
+}
 
 int
 tresize(int col, int row) {