Add new assert() statements in an attempt to help static analyzers avoid

false-positives.

FossilOrigin-Name: 9e66458592d40fbd96ea5f21339573110ca1cfe328238a020c9420a87d35dd72

src/wal.c

@@ -3478,6 +3478,7 @@ int sqlite3WalFrames(
         if( rc ) return rc;
         iOffset += szFrame;
         nExtra++;
+        assert( pLast!=0 );
       }
     }
     if( bSync ){
@@ -3510,6 +3511,7 @@ int sqlite3WalFrames(
     iFrame++;
     rc = walIndexAppend(pWal, iFrame, p->pgno);
   }
+  assert( pLast!=0 || nExtra==0 );
   while( rc==SQLITE_OK && nExtra>0 ){
     iFrame++;
     nExtra--;