memdb: Bug in insert algorithm causes SMR mode crash

oroutine 967 [runnable]:
_/Users/sarath/gocode/src/github.com/t3rm1n4l/memdb.newInsertCompare.func1(0xdddddddddddddddd, 0xc8203c2020, 0xdddddddddddddddd)
/Users/sarath/gocode/src/github.com/t3rm1n4l/memdb/memdb.go:94 +0x41
github.com/t3rm1n4l/memdb/skiplist.compare(0xc82000e630, 0xdddddddddddddddd, 0xc8203c2020, 0xffffffffffffff00)
/Users/Sarath/gocode/src/github.com/t3rm1n4l/memdb/skiplist/item.go:16 +0x5a
github.com/t3rm1n4l/memdb/skiplist.(*Skiplist).findPath(0xc820071a00, 0xc8203c2020, 0xc82000e630, 0xc82000a540, 0xc820071a18, 0x0)
/Users/Sarath/gocode/src/github.com/t3rm1n4l/memdb/skiplist/skiplist.go:194 +0x22d
github.com/t3rm1n4l/memdb/skiplist.(*Iterator).SeekWithCmp(0xc8203a5580, 0xc8203c2020, 0xc82000e630, 0xc82000e650, 0xc820496100)
/Users/Sarath/gocode/src/github.com/t3rm1n4l/memdb/skiplist/iterator.go:36 +0x61
_/Users/sarath/gocode/src/github.com/t3rm1n4l/memdb.(*Writer).GetNode(0xc8200bc000, 0xc820175ef0, 0xa, 0xa, 0x0)
/Users/sarath/gocode/src/github.com/t3rm1n4l/memdb/memdb.go:218 +0x125
_/Users/sarath/gocode/src/github.com/t3rm1n4l/memdb.(*Writer).Delete2(0xc8200bc000, 0xc820175ef0, 0xa, 0xa, 0xa, 0xa)
/Users/sarath/gocode/src/github.com/t3rm1n4l/memdb/memdb.go:226 +0x43
_/Users/sarath/gocode/src/github.com/t3rm1n4l/memdb.(*Writer).Delete(0xc8200bc000, 0xc820175ef0, 0xa, 0xa, 0xa)
/Users/sarath/gocode/src/github.com/t3rm1n4l/memdb/memdb.go:207 +0x3f
_/Users/sarath/gocode/src/github.com/t3rm1n4l/memdb.doReplace(0xc82000e6e0, 0xc820090120, 0xc8200bc000, 0x1d, 0x64)
/Users/sarath/gocode/src/github.com/t3rm1n4l/memdb/memdb_test.go:342 +0x1e4
created by _/Users/sarath/gocode/src/github.com/t3rm1n4l/memdb.TestGCPerf
/Users/sarath/gocode/src/github.com/t3rm1n4l/memdb/memdb_test.go:368 +0x256