Avoid initialization of vt100_0 in each call to tsetchar

If vt100_0 is a automatic variable then it is initializated in each call to
tsetchar, but if the variable is static it is initializated only in compile
time.
---
 st.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

st.c

@@ -1183,7 +1183,7 @@ tmoveto(int x, int y) {
 
 void
 tsetchar(char *c) {
-	char *vt100_0[62] = { /* 0x41 - 0x7e */
+	static char *vt100_0[62] = { /* 0x41 - 0x7e */
 		"↑", "↓", "→", "←", "█", "▚", "☃", /* A - G */
 		0, 0, 0, 0, 0, 0, 0, 0, /* H - O */
 		0, 0, 0, 0, 0, 0, 0, 0, /* P - W */