MatchRule: Prevent non-eating special characters from eating characters

Special characters such as N, S1, etc. are not actually eating
characters. Their treatment should thus *not* update pre_ptr and post_ptr,
otherwise those would underflow/overflow, e.g. in the case

@) s (_NS1  [z]

this would overflow. This for instance noticeable with the memory sanitizer:

ESPEAK_DATA_PATH=$PWD ./src/espeak-ng -qX "capitals"
Translate 'capitals'
  1	c        [k]

  1	a        [a]

  1	p        [p]

  1	i        [I]

  1	t        [t]

  1	a        [a]

  1	l        [l]
 20	l (C     [l]

==2837201==WARNING: MemorySanitizer: use-of-uninitialized-value
    #0 0x7f7f4422744b in utf8_in2 /home/samy/brl/speech/espeak-ng-git/src/libespeak-ng/translate.c:281:2
    #1 0x7f7f442281bc in utf8_in /home/samy/brl/speech/espeak-ng-git/src/libespeak-ng/translate.c:332:9
    #2 0x7f7f440e0d31 in MatchRule /home/samy/brl/speech/espeak-ng-git/src/libespeak-ng/dictionary.c:1767:21
    #3 0x7f7f440d937f in TranslateRules /home/samy/brl/speech/espeak-ng-git/src/libespeak-ng/dictionary.c:2320:6
    #4 0x7f7f44230e5f in TranslateWord3 /home/samy/brl/speech/espeak-ng-git/src/libespeak-ng/translate.c:733:15
    #5 0x7f7f44229844 in TranslateWord /home/samy/brl/speech/espeak-ng-git/src/libespeak-ng/translate.c:1100:14
    #6 0x7f7f44256e50 in TranslateWord2 /home/samy/brl/speech/espeak-ng-git/src/libespeak-ng/translate.c:1361:11
    #7 0x7f7f4424d6cc in TranslateClause /home/samy/brl/speech/espeak-ng-git/src/libespeak-ng/translate.c:2623:17
    #8 0x7f7f44213359 in SpeakNextClause /home/samy/brl/speech/espeak-ng-git/src/libespeak-ng/synthesize.c:1569:2
    #9 0x7f7f441a9f56 in Synthesize /home/samy/brl/speech/espeak-ng-git/src/libespeak-ng/speech.c:457:2
    #10 0x7f7f441a9023 in sync_espeak_Synth /home/samy/brl/speech/espeak-ng-git/src/libespeak-ng/speech.c:570:29
    #11 0x7f7f441ad59f in espeak_ng_Synthesize /home/samy/brl/speech/espeak-ng-git/src/libespeak-ng/speech.c:678:10
    #12 0x7f7f4410b3f4 in espeak_Synth /home/samy/brl/speech/espeak-ng-git/src/libespeak-ng/espeak_api.c:90:32
    #13 0x4a8be3 in main /home/samy/brl/speech/espeak-ng-git/src/espeak-ng.c:691:3
    #14 0x7f7f43a2e7fc in __libc_start_main csu/../csu/libc-start.c:332:16
    #15 0x421449 in _start (/home/samy/ens/projet/1/speech/espeak-ng-git/src/.libs/espeak-ng+0x421449)

  Uninitialized value was created by an allocation of 'sbuf' in the stack frame of function 'TranslateClause'
    #0 0x7f7f4423a1f0 in TranslateClause /home/samy/brl/speech/espeak-ng-git/src/libespeak-ng/translate.c:1941

While trying to match _NS1, MatchRule is overflowing the buffer.

It happens that this had not usually posed problem because rules usually
have these non-eating special characters last in the rule and thus it wasn't
mattering that post_ptr is pointing outside valid text.

src/libespeak-ng/dictionary.c

 						failed = 1;
 					break;
 				case RULE_DOLLAR:
+					post_ptr--;
 					command = *rule++;
 					if (command == DOLLAR_UNPR)
 						match.end_type = SUFX_UNPRON; // $unpron
 				}
 					break;
 				case RULE_INC_SCORE:
+					post_ptr--;
 					add_points = 20; // force an increase in points
 					break;
 				case RULE_DEC_SCORE:
+					post_ptr--;
 					add_points = -20; // force an decrease in points
 					break;
 				case RULE_DEL_FWD:
 				case RULE_NO_SUFFIX:
 					if (word_flags & FLAG_SUFFIX_REMOVED)
 						failed = 1; // a suffix has been removed
-					else
+					else {
+						post_ptr--;
 						add_points = 1;
+					}
 					break;
 				default:
 					if (letter == rb) {
 						failed = 1;
 					break;
 				case RULE_DOLLAR:
+					pre_ptr++;
 					command = *rule++;
 					if ((command == DOLLAR_LIST) || ((command & 0xf0) == 0x20)) {
 						// $list or $p_alt
 						failed = 1;
 					break;
 				case RULE_STRESSED:
+					pre_ptr++;
 					if (tr->word_stressed_count > 0)
 						add_points = 19;
 					else
 				}
 					break;
 				case RULE_IFVERB:
+					pre_ptr++;
 					if (tr->expect_verb)
 						add_points = 1;
 					else
 						failed = 1;
 					break;
 				case RULE_CAPITAL:
+					pre_ptr++;
 					if (word_flags & FLAG_FIRST_UPPER)
 						add_points = 1;
 					else