Core/Dependencies: Update utf8-cpp to version 2.3.4

dep/PackageList.txt

@@ -30,7 +30,7 @@ SFMT (SIMD-oriented Fast Mersenne Twister)
 
 utf8-cpp (UTF-8 with C++ in a Portable Way)
   http://utfcpp.sourceforge.net/
-  Version: 2.3.2
+  Version: 2.3.4
 
 zlib (A Massively Spiffy Yet Delicately Unobtrusive Compression Library)
   http://www.zlib.net/

dep/utf8cpp/utf8/checked.h

@@ -109,13 +109,13 @@ namespace utf8
                 case internal::NOT_ENOUGH_ROOM:
                     throw not_enough_room();
                 case internal::INVALID_LEAD:
-                    utf8::append (replacement, out);
+                    out = utf8::append (replacement, out);
                     ++start;
                     break;
                 case internal::INCOMPLETE_SEQUENCE:
                 case internal::OVERLONG_SEQUENCE:
                 case internal::INVALID_CODE_POINT:
-                    utf8::append (replacement, out);
+                    out = utf8::append (replacement, out);
                     ++start;
                     // just one replacement mark for the sequence
                     while (start != end && utf8::internal::is_trail(*start))
@@ -270,7 +270,7 @@ namespace utf8
       octet_iterator range_start;
       octet_iterator range_end;
       public:
-      iterator () {};
+      iterator () {}
       explicit iterator (const octet_iterator& octet_it,
                          const octet_iterator& range_start,
                          const octet_iterator& range_end) :

dep/utf8cpp/utf8/unchecked.h

@@ -179,7 +179,7 @@ namespace utf8
           class iterator : public std::iterator <std::bidirectional_iterator_tag, uint32_t> { 
             octet_iterator it;
             public:
-            iterator () {};
+            iterator () {}
             explicit iterator (const octet_iterator& octet_it): it(octet_it) {}
             // the default "big three" are OK
             octet_iterator base () const { return it; }