some tilemap.c cleanup

some tilemap.c cleanup

I'm headed back to the drawing board for some tiles changes I was
attempting, but before tossing what I had I've extracted a modest
amount of cleanup for the code in win/share/tilemap.c.  Some
formatting, a bit of generated formatting, make ENHANCED_SYMBOLS
less intrusive, and an error check to prevent a crash in tilemap
I triggered.  Also avoid one in nethack caused by an object (not
included here) which had a description but no name.