[jdk17u-dev] RFR: 8300079: SIGSEGV in LibraryCallKit::inline_string_copy due to constant NULL src argument

[Goetz Lindenmaier]

I backport this for parity with 17.0.8-oracle.

Does not apply because
"8275201: C2: hide klass() accessor from TypeOopPtr and typeKlassPtr subclasses" is not in 17.

The problem fixed by this change is that isa_aryptr() can return NULL.
I checked all occurances of this call. Many of them are checked for NULL which 
was missing in head before this fix. For inline_string_copy() the check was missing
in 17.
For many of the other checks, the result is assigned to a variable and then checked, 
but then isa_aryptr() is called again. I changed the code to use the checked variable.
I hope this makes clear that the check may not be removed :)

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Commit messages:
 - Backport 45e4e00981ef8b4bf143afce0889698319273c1d

Changes: https://git.openjdk.org/jdk17u-dev/pull/1297/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk17u-dev&pr=1297&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8300079
  Stats: 87 lines in 2 files changed: 61 ins; 0 del; 26 mod
  Patch: https://git.openjdk.org/jdk17u-dev/pull/1297.diff
  Fetch: git fetch https://git.openjdk.org/jdk17u-dev.git pull/1297/head:pull/1297

PR: https://git.openjdk.org/jdk17u-dev/pull/1297