+ fix crash on MS/Windows with files having an empty title (Alchemy.zim)

src/zimlib/src/cluster.cpp

@@ -105,10 +105,13 @@ namespace zim
     {
       n = offsets.back() - offsets.front();
       data.resize(n);
+      if (n > 0)
+      {
         log_debug1("read " << n << " bytes of data");
         in.read(&(data[0]), n);
       }
     }
+  }
 
   void ClusterImpl::write(std::ostream& out) const
   {
@@ -133,7 +136,8 @@ namespace zim
 
   Blob ClusterImpl::getBlob(size_type n) const
   {
-    return Blob(const_cast<ClusterImpl*>(this), getData(n), getSize(n));
+    return getSize(n) > 0 ?
+      Blob(const_cast<ClusterImpl*>(this), getData(n), getSize(n)) : Blob();
   }
 
   void ClusterImpl::clear()