[llvm] [Analysis] Fix null ptr dereference when using WriteGraph without branch probability info (PR #104102)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-ppc64le-linux-test-suite` running on `ppc64le-clang-test-suite` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/95/builds/2630

Here is the relevant piece of the build log for the reference:
```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'SanitizerCommon-msan-powerpc64le-Linux :: Linux/getpwnam_r_invalid_user.cpp' FAILED ********************
Exit Code: 134

Command Output (stderr):
--
RUN: at line 2: /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/build/./bin/clang  --driver-mode=g++ -gline-tables-only -fsanitize=memory  -m64 -fno-function-sections -funwind-tables  -I/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/llvm-project/compiler-rt/test -ldl -O0 -g /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/llvm-project/compiler-rt/test/sanitizer_common/TestCases/Linux/getpwnam_r_invalid_user.cpp -o /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/build/runtimes/runtimes-bins/compiler-rt/test/sanitizer_common/msan-powerpc64le-Linux/Linux/Output/getpwnam_r_invalid_user.cpp.tmp &&  /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/build/runtimes/runtimes-bins/compiler-rt/test/sanitizer_common/msan-powerpc64le-Linux/Linux/Output/getpwnam_r_invalid_user.cpp.tmp
+ /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/build/./bin/clang --driver-mode=g++ -gline-tables-only -fsanitize=memory -m64 -fno-function-sections -funwind-tables -I/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/llvm-project/compiler-rt/test -ldl -O0 -g /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/llvm-project/compiler-rt/test/sanitizer_common/TestCases/Linux/getpwnam_r_invalid_user.cpp -o /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/build/runtimes/runtimes-bins/compiler-rt/test/sanitizer_common/msan-powerpc64le-Linux/Linux/Output/getpwnam_r_invalid_user.cpp.tmp
+ /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/build/runtimes/runtimes-bins/compiler-rt/test/sanitizer_common/msan-powerpc64le-Linux/Linux/Output/getpwnam_r_invalid_user.cpp.tmp
getpwnam_r_invalid_user.cpp.tmp: /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/llvm-project/compiler-rt/test/sanitizer_common/TestCases/Linux/getpwnam_r_invalid_user.cpp:17: int main(): Assertion `res == 0 || res == ENOENT' failed.
/home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/build/runtimes/runtimes-bins/compiler-rt/test/sanitizer_common/msan-powerpc64le-Linux/Linux/Output/getpwnam_r_invalid_user.cpp.script: line 1: 3986898 Aborted                 /home/buildbots/llvm-external-buildbots/workers/ppc64le-clang-test-suite/clang-ppc64le-test-suite/build/runtimes/runtimes-bins/compiler-rt/test/sanitizer_common/msan-powerpc64le-Linux/Linux/Output/getpwnam_r_invalid_user.cpp.tmp

--

********************


```

https://github.com/llvm/llvm-project/pull/104102