There is a couple of newGenericDecompressor function usages, where
returned possibly non-nil `err` is not checked before dereferencing
returned decompressor. It may lead to nil ptr dereferencing.
This commit adds check for `err` to prevent dereferencing potentially
nullable decompressor.
Found by Linux Verification Center (linuxtesting.org) with SVACE
Signed-off-by: Mikhail Dmitrichenko <m.dmitrichenko222@gmail.com>
fdc738b0df