segment.cpp: Avoid comparisons of (un)signed integers

algo/core/segment.cpp

@@ -804,9 +804,9 @@ void FineSegmenter::findCDR3(){
     std::list<string>::const_iterator it;
     for (it = codon_start.begin(); it != codon_start.end(); ++it) {//filter 1 : start codon must be in V
         loc = 0;
-        while ( loc != string::npos & loc < Vend){
+        while ( loc != string::npos & loc < (size_t)Vend){
             loc = str.find(*it, loc+3);
-            if (loc != string::npos & loc < Vend) {
+            if (loc != string::npos & loc < (size_t)Vend) {
                 p_start.push_front(loc);
             }
         }