Fix that if BINDIR is empty CMake does not fail

Signed-off-by: Martin Melik-Merkumians <melik-merkumians@acin.tuwien.ac.at>

source/src/ports/POSIX/CMakeLists.txt

@@ -65,4 +65,6 @@ if( NOT OpENer_TESTS)
   endif()
 endif()
 
-install (PROGRAMS ${CMAKE_CURRENT_BINARY_DIR}/OpENer DESTINATION ${CMAKE_INSTALL_BINDIR})
+if(NOT ${CMAKE_INSTALL_BINDIR} STREQUAL "")
+  install (PROGRAMS ${CMAKE_CURRENT_BINARY_DIR}/OpENer DESTINATION ${CMAKE_INSTALL_FULL_BINDIR})
+endif()