Fix 4-digit bug in separat_thousand() used for 'T' @-code format modifier

I noticed while testing the previous commit that 4 digit values weren't
thousands-separated, while larger values were. I'm not sure why this
non-zero index check was in this loop, but appears to be a bug.

src/sbbs3/atcodes.cpp

@@ -46,7 +46,7 @@ static char* separate_thousands(const char* src, char *dest, size_t maxlen, char
 	char* d = dest;
 	for(size_t i = 0; i < digits; d++, i++) {
 		*d = src[i];
-		if(i && i + 3 < digits && (digits - (i + 1)) % 3 == 0)
+		if(i + 3 < digits && (digits - (i + 1)) % 3 == 0)
 			*(++d) = sep;
 	}
 	*d = 0;