Fix: backend processing was not treating ${} as a special pcre character

Also for characters that are not recognized as a valid escape seq
make sure that the character is emitted.

previously
  \$ resulted in \
where it should have been \$ if $ wasn't recognized

Signed-off-by: John Johansen <john.johansen@canonical.com>
Acked-by: Steve Beattie <steve@nxnw.org>

parser/libapparmor_re/parse.y

@@ -172,14 +172,15 @@ int regex_lex(YYSTYPE *val, const char **pos)
 		return *(*pos - 1);
 
 	case '\\':
-		tmp = str_escseq(pos, "*+.|^-[]()");
-		if (tmp == -1)
+		tmp = str_escseq(pos, "*+.|^$-[](){}");
+		if (tmp == -1) {
 			/* bad escape sequence, just skip it for now, that
 			 * is output \\ followed by the invalid esc seq
 			 * TODO: output error message
 			 */
 			val->c = '\\';
-		else
+			(*pos)--;
+		} else
 			val->c = tmp;
 		break;
 	}