RFR: 8315739: Missing null check in os::vm_min_address [v2]

[Daniel Jeliński]

> Please review this fix for handling of file `/proc/sys/vm/mmap_min_addr` which does not exist on WSL1.
> 
> This fixes a crash if the file is absent, and a file handle leak (missing `fclose`) when the file is present.
> 
> Linux tier1 tests clean.

Daniel Jeliński has updated the pull request incrementally with one additional commit since the last revision:

  move MAX after fclose

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/15596/files
  - new: https://git.openjdk.org/jdk/pull/15596/files/058c7749..e330c334

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15596&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15596&range=00-01

  Stats: 4 lines in 1 file changed: 1 ins; 3 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/15596.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15596/head:pull/15596

PR: https://git.openjdk.org/jdk/pull/15596