enca: fix compiler warnings for GCC with -Wunused-but-set-variable

[heitbaum]

Variable 'map_created' in xtable() is only used in assert() which is compiled out when -DNDEBUG is defined. Wrap the block in #ifndef NDEBUG to preserve debug-build sanity checking while silencing the warning in release builds.

[Syed-Shahrukh-OSSRevival]

Thank you for your contribution, makes sense.
You can utilize DEBUG.

changelog entry

2003-06-24  David Necas (Yeti) <yeti@physics.muni.cz>
    * lib/internal.h: added enca_csname macro and #include <stdio.h> when
      DEBUG is defined