Prevent infinite looping in GetString on certain malformed strings

[bridgetlane]

Description: This PR is to address the open issue: #164

Benchmark before change:

goos: darwin
goarch: amd64
pkg: github.com/buger/jsonparser/benchmark
BenchmarkJsonParserLarge-8 200000 49082 ns/op 0 B/op 0 allocs/op
BenchmarkJsonParserMedium-8 1000000 7254 ns/op 0 B/op 0 allocs/op
BenchmarkJsonParserDeleteMedium-8 1000000 7638 ns/op 0 B/op 0 allocs/op
BenchmarkJsonParserEachKeyManualMedium-8 1000000 5123 ns/op 112 B/op 2 allocs/op
BenchmarkJsonParserEachKeyStructMedium-8 1000000 5726 ns/op 544 B/op 12 allocs/op
BenchmarkJsonParserObjectEachStructMedium-8 1000000 7774 ns/op 496 B/op 11 allocs/op
BenchmarkJsonParserSmall-8 10000000 766 ns/op 0 B/op 0 allocs/op
BenchmarkJsonParserEachKeyManualSmall-8 10000000 616 ns/op 80 B/op 2 allocs/op
BenchmarkJsonParserEachKeyStructSmall-8 10000000 1192 ns/op 192 B/op 8 allocs/op
BenchmarkJsonParserObjectEachStructSmall-8 10000000 784 ns/op 176 B/op 7 allocs/op
BenchmarkJsonParserSetSmall-8 10000000 1105 ns/op 768 B/op 4 allocs/op
BenchmarkJsonParserDelSmall-8 5000000 1388 ns/op 0 B/op 0 allocs/op
PASS
ok github.com/buger/jsonparser/benchmark 101.571s

Benchmark after change:

goos: darwin
goarch: amd64
pkg: github.com/buger/jsonparser/benchmark
BenchmarkJsonParserLarge-8 200000 47197 ns/op 0 B/op 0 allocs/op
BenchmarkJsonParserMedium-8 1000000 7353 ns/op 0 B/op 0 allocs/op
BenchmarkJsonParserDeleteMedium-8 1000000 7470 ns/op 0 B/op 0 allocs/op
BenchmarkJsonParserEachKeyManualMedium-8 1000000 5169 ns/op 112 B/op 2 allocs/op
BenchmarkJsonParserEachKeyStructMedium-8 1000000 5568 ns/op 544 B/op 12 allocs/op
BenchmarkJsonParserObjectEachStructMedium-8 1000000 7740 ns/op 496 B/op 11 allocs/op
BenchmarkJsonParserSmall-8 10000000 750 ns/op 0 B/op 0 allocs/op
BenchmarkJsonParserEachKeyManualSmall-8 20000000 621 ns/op 80 B/op 2 allocs/op
BenchmarkJsonParserEachKeyStructSmall-8 10000000 835 ns/op 192 B/op 8 allocs/op
BenchmarkJsonParserObjectEachStructSmall-8 10000000 721 ns/op 176 B/op 7 allocs/op
BenchmarkJsonParserSetSmall-8 10000000 1100 ns/op 768 B/op 4 allocs/op
BenchmarkJsonParserDelSmall-8 5000000 1565 ns/op 0 B/op 0 allocs/op
PASS
ok github.com/buger/jsonparser/benchmark 104.016s

For running benchmarks use:

go test -test.benchmem -bench JsonParser ./benchmark/ -benchtime 5s -v
# OR
make bench (runs inside docker)