RFR: 8331731: ubsan: relocInfo.cpp:155:30: runtime error: applying non-zero offset to null pointer

[Vladimir Kozlov]

Avoid iterations on empty relocation info. Found by running `ubsan`.

Tested tier1-4, stress, xcomp.

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Commit messages:
 - 8331731: ubsan: relocInfo.cpp:155:30: runtime error: applying non-zero offset to null pointer

Changes: https://git.openjdk.org/jdk/pull/19525/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=19525&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8331731
  Stats: 8 lines in 2 files changed: 1 ins; 4 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/19525.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/19525/head:pull/19525

PR: https://git.openjdk.org/jdk/pull/19525