decode: Fix walk root depth issue causing dump to indent incorrectly

pkg/decode/value.go

@@ -90,7 +90,8 @@ func (v *Value) Walk(opts WalkOpts) error {
 		}
 
 		rootDepthDelta := 0
-		if wv.IsRoot {
+		// only count switching to a new root
+		if wv.IsRoot && wv != rootV {
 			rootV = wv
 			rootDepthDelta = 1
 		}

pkg/interp/dump.go

@@ -322,10 +322,6 @@ func dump(v *decode.Value, w io.Writer, opts Options) error {
 			if opts.Depth != 0 && depth > opts.Depth {
 				return decode.ErrWalkSkipChildren
 			}
-			// skip first root level
-			if rootDepth > 0 {
-				rootDepth--
-			}
 
 			return fn(v, rootV, depth, rootDepth)
 		}

pkg/interp/testdata/display.fqtest

@@ -427,3 +427,4 @@ $ fq -n '"broken" | mp3 | d'
    |                                               |                |  headers: [0]
    |                                               |                |  frames: [0]
 0x0|62 72 6f 6b 65 6e|                             |broken|         |  unknown0: raw bits
+# TODO: add root depth test