Fix further problems with fts5 and corrupt databases causing integer overflow.

FossilOrigin-Name: 673a7dd698eca05bb2909fa01f962a0667361732a6d0e61cf7780ead4a07c967

ext/fts5/fts5_index.c

@@ -2234,10 +2234,10 @@ static void fts5LeafSeek(
   int szLeaf = pIter->pLeaf->szLeaf;
   int n = pIter->pLeaf->nn;
 
-  int nMatch = 0;
-  int nKeep = 0;
-  int nNew = 0;
-  int iTermOff;
+  u32 nMatch = 0;
+  u32 nKeep = 0;
+  u32 nNew = 0;
+  u32 iTermOff;
   int iPgidx;                     /* Current offset in pgidx */
   int bEndOfPage = 0;