Use 0x40 (ASCII '@') instead of 0x00 to mean "no affinity" so that columns

with no affinity can appear in a zero-terminated string.  Use the new
SQLITE_AFF_NONE macro for this new magic number.

FossilOrigin-Name: e8234f6939ccff4c10f741cf66d1c537cfebcbd0d1d79a618a64c755a7f087b5

src/where.c

@@ -1305,6 +1305,7 @@ char sqlite3IndexColumnAffinity(sqlite3 *db, Index *pIdx, int iCol){
   if( !pIdx->zColAff ){
     if( sqlite3IndexAffinityStr(db, pIdx)==0 ) return SQLITE_AFF_BLOB;
   }
+  assert( pIdx->zColAff[iCol]!=0 );
   return pIdx->zColAff[iCol];
 }
 #endif