Fix a bug introduced with recent optimizations:  The unary minus operator
is TK_UMINUS, not TK_MINUS.

FossilOrigin-Name: 4bd43307090258f8652c995b056101c51b81274a
diff --git a/src/expr.c b/src/expr.c
index 99d88f9..fbb456f 100644
--- a/src/expr.c
+++ b/src/expr.c
@@ -1274,7 +1274,7 @@
 */
 int sqlite3ExprCanBeNull(const Expr *p){
   u8 op;
-  while( p->op==TK_UPLUS || p->op==TK_MINUS ){ p = p->pLeft; }
+  while( p->op==TK_UPLUS || p->op==TK_UMINUS ){ p = p->pLeft; }
   op = p->op;
   if( op==TK_REGISTER ) op = p->op2;
   switch( op ){
@@ -1319,7 +1319,7 @@
 int sqlite3ExprNeedsNoAffinityChange(const Expr *p, char aff){
   u8 op;
   if( aff==SQLITE_AFF_NONE ) return 1;
-  while( p->op==TK_UPLUS || p->op==TK_MINUS ){ p = p->pLeft; }
+  while( p->op==TK_UPLUS || p->op==TK_UMINUS ){ p = p->pLeft; }
   op = p->op;
   if( op==TK_REGISTER ) op = p->op2;
   switch( op ){