MatchRule: Support multibyte doubled letters

When matching a double-letter whose encoding needs multiple bytes, to
properly skip the double-letter we have to skip these bytes, like other
rules.

src/libespeak-ng/dictionary.c

 						failed = 1;
 					break;
 				case RULE_DOUBLE:
-					if (letter_w == last_letter_w)
+					if (letter_w == last_letter_w) {
 						add_points = (21-distance_right);
-					else
+						post_ptr += letter_xbytes;
+					} else
 						failed = 1;
 					break;
 				case RULE_DOLLAR:
 						failed = 1;
 					break;
 				case RULE_DOUBLE:
-					if (letter_w == last_letter_w)
+					if (letter_w == last_letter_w) {
 						add_points = (21-distance_left);
-					else
+						pre_ptr -= letter_xbytes;
+					} else
 						failed = 1;
 					break;
 				case RULE_DIGIT: