Initialize a variable in fts3_write.c on the grounds that the argument required to show that it does not require initialization with is complicated. Add an assert() to where.c to silence a clang scan-build warning.

FossilOrigin-Name: d6c4d48a002a6d7057fccc30064ce0b049678f0c

src/where.c

@@ -4482,6 +4482,7 @@ static Bitmask columnsInIndex(Index *pIdx){
   int j;
   for(j=pIdx->nColumn-1; j>=0; j--){
     int x = pIdx->aiColumn[j];
+    assert( x>=0 );
     testcase( x==BMS-1 );
     testcase( x==BMS-2 );
     if( x<BMS-1 ) m |= MASKBIT(x);