fix assignment operator against nested slicing

cli/test.yaml

@@ -3210,7 +3210,9 @@
 - name: assignment operator against array with slice
   args:
     - -c
-    - '.[2:4] = ([], [0], [4,3,2]), .[1:-1] = [3,2], .[2:0] = [.[]], .[10:] = [1], .[-20:-10] = [1]'
+    - '.[2:4] = ([], [0], [4,3,2]), .[1:-1] = [3,2], .[2:0] = [.[]], .[10:] = [1],
+       .[-20:-10] = [1], .[0:5] = [9], .[1:][1:] = [9], .[1:][:3] = [6,7,8],
+       .[:4][1:][:3] = [9], .[1:][1:-2] = [9], .[:4][-3:][:5] = [9], (null | .[:1][2:] = [9])'
   input: '[1,2,3,4,5]'
   expected: |
     [1,2,5]
@@ -3220,6 +3222,13 @@
     [1,2,1,2,3,4,5,3,4,5]
     [1,2,3,4,5,1]
     [1,1,2,3,4,5]
+    [9]
+    [1,2,9]
+    [1,6,7,8,5]
+    [1,9,5]
+    [1,2,9,4,5]
+    [1,9,5]
+    [9]
 
 - name: assignment operator deeply
   args:

func.go

@@ -1257,24 +1257,16 @@ func updatePaths(v interface{}, path []interface{}, w interface{}, delpaths bool
 			}
 			if x, ok := toInt(x["end"]); ok {
 				x := toIndex(uu, x)
-				if x < start {
+				if x == -1 {
+					end = len(uu)
+				} else if x < start {
 					end = start
 				} else {
 					end = x
 				}
 			} else {
 				end = len(uu)
 			}
-			if len(path) > 1 {
-				u, err := updatePaths(uu[start], path[1:], w, delpaths)
-				if err != nil {
-					return nil, err
-				}
-				vs := make([]interface{}, len(uu))
-				copy(vs, uu)
-				vs[start] = u
-				return vs, nil
-			}
 			if delpaths {
 				if start >= end {
 					return uu, nil
@@ -1286,6 +1278,13 @@ func updatePaths(v interface{}, path []interface{}, w interface{}, delpaths bool
 				}
 				return vs, nil
 			}
+			if len(path) > 1 {
+				u, err := updatePaths(uu[start:end], path[1:], w, delpaths)
+				if err != nil {
+					return nil, err
+				}
+				w = u
+			}
 			switch v := w.(type) {
 			case []interface{}:
 				vs := make([]interface{}, start+len(v)+len(uu)-end)