ANDROID: fuse-bpf: Add NULL pointer check in fuse_release_in

If open request sent to classic fuse, backing_file is null.
In fuse_release_initialize, fput will trigger a crash.

Bug: 297831741
Signed-off-by: liujing40 <liujing40@xiaomi.corp-partner.google.com>
(cherry picked from https://android-review.googlesource.com/q/commit:4d2ff573981f06ba09e1ddda8726bb73ff6a2c3f)
Merged-In: I2d54d99d62b54c39a6dc9064f8f62488433aff6f
Change-Id: I2d54d99d62b54c39a6dc9064f8f62488433aff6f