Don't advance active successor's frame in phone_transition

When phone_transition fires and the successor HMM is already active
(hmm_frame >= frame_idx), calling hmm_enter() overwrites hmm_frame
with nf even though the phone is already being tracked at the current
frame.  Split the entry into two cases: inactive successors get a
full hmm_enter() with the new frame assignment; active ones only have
their in_score and in_history updated if the incoming score is better.
This is the correct Viterbi competition rule.

Author: lenzo-ka

src/state_align_search.c

@@ -121,11 +121,14 @@ phone_transition(state_align_search_t *sas, int frame_idx)
             continue;
 
         newphone_score = hmm_out_score(hmm);
-        /* Transition into next phone using the usual Viterbi rule. */
         nhmm = hmm + 1;
-        if (hmm_frame(nhmm) < frame_idx
-            || newphone_score BETTER_THAN hmm_in_score(nhmm)) {
+        if (hmm_frame(nhmm) < frame_idx) {
             hmm_enter(nhmm, newphone_score, hmm_out_history(hmm), nf);
+            continue;
+        }
+        if (newphone_score BETTER_THAN hmm_in_score(nhmm)) {
+            hmm_in_score(nhmm) = newphone_score;
+            hmm_in_history(nhmm) = hmm_out_history(hmm);
         }
     }
 }