OSV-2018-12 Heap-double-free in RMFRasterBand::IReadBlock

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=9138 Crash type: Heap-double-free Crash state: RMFRasterBand::IReadBlock GDALRasterBand::GetLockedBlockRef GDALRasterBand::IRasterIO...