Fix compile for GCC 5.1.0

Add fix for compile error with multiple uses of peerid_type (uint64_t)
variable in lambda expression.
- known GCC issue: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65843

epee: replace return value of nullptr for expected boolean with false.

Fixes #231.

contrib/epee/include/storages/portable_storage.h

@@ -427,7 +427,7 @@ namespace epee
       TRY_ENTRY();
       CHECK_AND_ASSERT(hsec_array, false);
       if(hsec_array->type() != typeid(array_entry_t<section>))
-        return nullptr;
+        return false;
       array_entry_t<section>& sec_array = boost::get<array_entry_t<section>>(*hsec_array);
       h_child_section = sec_array.get_next_val();
       if(!h_child_section)