[snapshot] SnapshotDiff should not accept continuation token greater than the length of the actual snapdiff

Steps :

• Create volume/bucket
• Create 1 key and create snapshot snap1
• Create 155 more keys and create snapshot snap160
• Execute snapshotDiff with continuation token 150
• Execute snapshotDiff with continuation token 200

Observed behaviour - 

SnapshotDiff lists till end of diff and gives next continuation token

# ozone sh snapshot diff -p 5 -t 150 vol1/buck1 snap1 snap160
Difference between snapshot: snap1 and snapshot: snap160
+    ./key156
+    ./key157
+    ./key158
+    ./key159
+    ./key160
Next token: 155 

SnapshotDiff does not list any items in the diff when continuation token is more than actual diff

# ozone sh snapshot diff -p 5 -t 200 vol1/buck1 snap1 snap160
Difference between snapshot: snap1 and snapshot: snap160 

Expected behaviour -

SnapshotDiff should reject when continuation token is more than actual diff. Also when snapshotDiff has reached the end limit of diff, it should not return any continuation token.