fix RowDiffere initialization

bats/keyless.bats

@@ -189,9 +189,9 @@ SQL
     run dolt --keyless sql -q "
         SELECT to_c0, to_c1, from_c0, from_c1
         FROM dolt_diff_keyless
-        WHERE from_commit = hashof('HEAD')
         ORDER BY to_commit_date" -r csv
     [ $status -eq 0 ]
+    [ "${#lines[@]}" -eq 11 ]
     [[ "${lines[0]}"  = "to_c0,to_c1,from_c0,from_c1"  ]] || false
     [[ "${lines[1]}"  = "8,8,,"  ]] || false
     [[ "${lines[2]}"  = ",,1,1"  ]] || false
@@ -199,6 +199,10 @@ SQL
     [[ "${lines[4]}"  = "1,9,,"  ]] || false
     [[ "${lines[5]}"  = "1,9,,"  ]] || false
     [[ "${lines[6]}"  = ",,0,0"  ]] || false
+    [[ "${lines[7]}"  = "1,1,,"  ]] || false
+    [[ "${lines[8]}"  = "1,1,,"  ]] || false
+    [[ "${lines[9]}"  = "0,0,,"  ]] || false
+    [[ "${lines[10]}" = "2,2,,"  ]] || false
 }
 
 @test "keyless diff column add/drop" {

go/libraries/doltcore/diff/async_differ.go

@@ -41,9 +41,12 @@ type RowDiffer interface {
 
 func NewRowDiffer(ctx context.Context, fromSch, toSch schema.Schema, buf int) RowDiffer {
 	ad := NewAsyncDiffer(buf)
-	if schema.IsKeyless(fromSch) && schema.IsKeyless(toSch) {
+
+	// assumes no PK changes
+	if schema.IsKeyless(fromSch) || schema.IsKeyless(toSch) {
 		return &keylessDiffer{AsyncDiffer: ad}
 	}
+
 	return ad
 }