Add a new assert() to help static analyzers understand that a pointer is

never NULL.

FossilOrigin-Name: 433f2b942ee6f79d50ebe9b08fa3ea8162db6a10ce9d80e2bc193124baa1b083

src/vdbesort.c

@@ -563,6 +563,7 @@ static int vdbePmaReadBlob(
       rc = vdbePmaReadBlob(p, nCopy, &aNext);
       if( rc!=SQLITE_OK ) return rc;
       assert( aNext!=p->aAlloc );
+      assert( aNext!=0 );
       memcpy(&p->aAlloc[nByte - nRem], aNext, nCopy);
       nRem -= nCopy;
     }