convert: fix tensor sorting (#12015)

there's two bugs here.

1. the check for a layer id is incorrect and should be >= 0 since layer
   0 is valid
2. if both tensors have an layer identifier, it will only compare the
   layer id which will return 0 if the tensors are in the same layer.
   instead it should fallback to comparing the full tensor name

fs/ggml/ggml.go

@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"io"
 	"log/slog"
+	"math"
 	"slices"
 	"strings"
 
@@ -276,7 +277,7 @@ type Tensor struct {
 
 func (t Tensor) block() (n int) {
 	if _, err := fmt.Sscanf(t.Name, "blk.%d.", &n); err != nil {
-		return -1
+		return math.MaxInt
 	}
 
 	return